Transcript Reading Part 5: The Nervous System
Unit 3: Control Systems of the Human Body
Dr. Achilly
Part 1: Nervous Tissue
“Concepts” chapter 14
Nervous System--overview
One of the smallest, but most complex body systems.
Made of: Brain Cranial nerves —12 pairs emerge from base of brain.
Spinal cord vertebrae.
—connects to the brain thru foramen magnum in skull & is encircled by
Nervous System--overview
Spinal nerves —emerge from spinal cord & serve specific regions of body.
Ganglia —masses of nerve tissue (mainly neuron cell bodies) outside brain or spinal cord.
Enteric plexuses —networks of neurons that regulate the digestive system.
Sensory receptors —ends of sensory neurons that monitor internal or external environmental changes.
Nervous System--overview
Nervous System--overview
Nervous system has 3 basic fxns: Sensory —detects internal & external stimuli. Carries this info to brain & spinal cord.
Integrative —the analyzing, storing & responding to sensory info.
Motor —carry out appropriate response like myo contraction or gland secretion. Info is carried from brain or spinal cord to effectors.
Nervous System--overview
The two main divisions of the nervous system are: Central nervous system (CNS) —consisting of brain and spinal cord Peripheral nervous system (PNS) —all the nervous tissue outside of CNS
Nervous System--overview
PNS can be further divided: Somatic nervous system —carries sensory fibers from head, body wall, limbs, special senses, etc. Also carries motor neurons to skeletal myos.
Nervous System--overview
Autonomic nervous system —carries sensory neurons from most of the organs and motor neurons to smooth & cardiac myo and glands.
The ANS can be further divided into the
sympathetic division
which handles “flight or fight” responses and the
parasympathetic division
“rest and digest” responses.
for
Nervous Tissue
The functional unit of the nervous system is the neuron.
It has electrical excitability & can propagate an electrical signal called an action potential.
Various sizes, but all contain similar parts.
Nervous Tissue
Cell body —contains nucleus, cytoplasm, all other cellular organelles.
Dendrites —these are the receiving fibers of the neuron. Usually many of them.
Axon —propagates action potential away from cell body toward another neuron. Usually singular. Place where the axon joins the cell body is an important area called axon hillock.
Nervous Tissue
Nervous Tissue
Nervous Tissue
The end of each axon contains many fine projections called axon terminals.
From here a neuron can communicate with another thru the synapse (the gap between neurons).
The axon terminal contains many membrane enclosed sacs called synaptic vesicles. They store many types of neurotransmitters which are chemicals that help the electrical impulse cross the synaptic gap btwn neurons.
Nervous Tissue
Nervous Tissue
Many axons are surrounded by a lipid & protein covering called a myelin sheath.
The sheath electrically insulates an axon & speeds conduction. Also aides in regeneration of injured neurons.
In the PNS the myelin is produced by a support cell called a Schwann cell. Gaps in Schwann cells are called nodes of Ranvier.
Nervous Tissue
Nervous Tissue
In CNS it’s the oligodendrocytes that myelinate the axons.
Little re-growth after injury.
Amount of myelin increases from birth to maturity.
Nervous Tissue
The areas of the nervous system that have myelinated axons appear white (white matter).
Areas of neuronal cell bodies, dendrites & unmyelinated axons appear gray (gray matter).
Nervous Tissue
In addition to neurons, about ½ the nervous system consists of support cells called neuroglia.
These cells do not propagate electrical impulses. Can divide & “fill in” areas of injury.
Nervous Tissue
Neuroglia of CNS Astrocytes —give structural support, wrap around capillaries of brain to form blood-brain barrier Oligodendrocytes —form myelin Microglia —fxn as phagocytes to remove cellular debris Ependymal cells —produce & circulate cerebral spinal fluid which nourishes the brain and spinal cord.
Nervous Tissue
Nervous Tissue
Neuroglia of PNS Schwann cells —form myelin Satellite cells —surround neuron cell bodies. Regulate exchange of materials btwn them & interstitial fluid (the fluid found surrounding all cells).
Electrical Signals
Production of nerve impulses depends on two features of the plasma 1.
membrane.
Membrane potential —the separation of ions across the membrane leading to an electrical voltage difference.
2.
Specific ion channels.
Electrical Signals
When ion channels are open, ions will move down their concentration gradient thru the channels & according to charge (+ towards -, and vice versa) The opening or closing of ion channels is due to presence of “gates.” Four types of channels:
Electrical Signals
Leakage channels randomly alternate btwn opened & closed.
Usually there are more K+ channels than Na+. Also K+ ones are “leakier.” Result is higher membrane permeability to K+.
Voltage gated channels open in response to change in membrane potential (voltage).
Electrical Signals
Ligand-gated channels open/close in response to specific molecules that bind to the channels. E.g. neurotransmitter binding to it
Electrical Signals
Mechanically gated channel opens/closes in response to mechanical stimulation: Vibration Pressure Stretch
Electrical Signals
Resting membrane potential Exists b/c of build up of (-) ions just inside the neuron cell membrane & (+) ions outside.
Separation of charges is a form of potential energy. About -70mV in a typical cell.
Dominant cation inside is K+, many anions (phosphates, amino acids) also. K+ can leak out, anions can’t.
Electrical Signals
Negative ions inside cell work to attract K+ back in.
Eventually an equal # of K+ ions enter & leave.
Na+ leaks inward a little.
Na+/K+ pump maintains charge difference.
At rest, the inside of a neuron's membrane has a negative charge. As the figure shows, a Na+ / K+ pump in the cell membrane pumps sodium out of the cell and potassium into it. However, because the cell membrane is a bit leakier to potassium than it is to sodium, more potassium ions leak out of the cell. As a result, the inside of the membrane builds up a net negative charge relative to the outside.
Electrical Signals
Graded potentials Arises when a stimulus causes a ligand or mechanically gated channel to open or close.
Depending on the type of ion channel opened, the membrane can become more negative (hyperpolarized) or more positive (depolarized).
Electrical Signals
These signals are “graded” b/c they vary in size depending on the strength of the stimulus.
Large stimulus more gates open Ion flow is localized, so it’s only useful for communication over short distances.
Usually present in dendrites.
Electrical Signals
Action Potentials Has depolarization & repolarization phases All or nothing response once threshold is reached.
Before an AP begins the membrane is at its resting potential.
The only movement of ions is thru leakage gates.
Electrical Signals
At rest both Na + & K + gated channels are closed; membrane is at -70mV resting potential.
Electrical Signals
A stimulus opens some Na + channels. The # of channels opened depends on the strength of the stimulus. If enough channels are opened, the inside of the neuron becomes slightly positively charged b/c of all the Na + flowing in.
Electrical Signals
Depolarization —so many Na + channels are open that the inside of cell becomes very positive. Positive feedback is involved here. In other words, the more positive the inside becomes, the more Na+ gates that open and so on.
Electrical Signals
Repolarization —finally K + gates open & K + rushes out. At the same time Na + gates close.
Electrical Signals
Undershoot —so much K + leaves the cell that it becomes more negative than the original resting potential. K + gates close. This phase is also called a refractory period. Another AP cannot occur in this portion of the membrane until Na/K pumps can restore the original ion concentration gradient & resting potential.
Electrical Signals
In order to relay information the AP must travel all the way down the axon. Called propagation.
When one segment of the membrane depolarizes the flood of Na + causes gated channels in the next section to open, etc.
Called continuous conduction.
Electrical Signals
In myelinated axons conduction is faster b/c only the nodes of Ranvier must depolarize.
Impulse “jumps” from node to node. Called saltatory conduction.
Electrical Signals
Once an AP reaches the terminus of the axon it must be passed on to the next cell across the synapse.
Some cells have direct connections btwn them (gap junctions —like tunnels btwn cells). Ions can flow from one cell to another.
Called electrical synapse.
Faster, synchronized (e.g. heart, viscera)
Electrical Signals
Many cells don’t have direct connections for ion flow.
The space btwn them is called synaptic cleft.
A chemical transmitter is required to cross the gap btwn neurons.
Called chemical synapse.
Electrical Signals
AP arrives at axon terminus of presynaptic neuron.
The depolarization here opens voltage gated Ca ++ channels.
The influx of Ca ++ causes exocytosis of synaptic vesicles that are filled with neurotransmitters.
Electrical Signals
Neurotransmitter diffuses across cleft & binds to receptors on postsynaptic neuron.
Often the receptors are ligand-gated ion channels which open to let ions in.
If the channels are for Na+, a depolarization of the membrane will occur.
If the channels are for K+ or Cl-, hyperpolarization will occur.
If threshold is reached, another AP begins.
Electrical Signals
Removal of neurotransmitter from cleft is essential.
Diffusion Degraded by enzymes Cellular re-uptake
Neurotransmitters
About 100 Some act quickly, others are slow.
Many are also hormones.
Two types: Small molecule Acetylcholine —excitatory to skeletal myo’s GABA —inhibitory in CNS Dopamine —active in neurons that govern emotions, addictive behavior
Neurotransmitters
Neuropeptides Endorphins —natural painkiller, euphoria Substance P —released by neurons that transmit pain-related input from peripheral receptors.
Part 2: Spinal Cord & Spinal Nerves
“Concepts” chapter 15 & 16
Spinal Cord & Spinal Nerves
Spinal cord is vital part of CNS Mediates some of our most rapid, reflex responses Integrates signals Serves as direct path to the brain for sensory input & motor output
Spinal cord anatomy
Vertebral column serves as bony protection for spinal cord.
Cord is also surrounded by 3 layers of tough connective tissue called meninges.
Dura matter Arachnoid matter Pia matter The spaces btwn these layers contain fluid (cerebral spinal fluid).
Spinal cord anatomy
Extends from medulla oblongata to L2.
Two obvious enlargements Cervical (C4-T1) —nerves to upper limb arise here.
Lumbar (T9-T12) —nerves to lower limb Cord tapers at L2 to form conus medullaris.
An extension of the pia matter anchors the cord to the coccyx. Called filum terminale.
Nerves that arise from lower end of cord angle downward before they exit vert. column. Form cauda equina.
Spinal cord anatomy
Spinal nerves are formed from 2 bundles of axons called roots.
Spinal cord anatomy
Posterior (dorsal) root = sensory neurons Has an enlarged area where the neuron cell bodies are. Called ganglion.
Anterior (ventral) root = motor neurons
Spinal cord anatomy
Two grooves divide cord into R & L halves: Anterior median fissure Posterior median sulcus White matter surrounds gray.
Gray matter is the innermost part. Shaped like an H.
Spinal cord anatomy
Gray matter is collection of cell bodies.
Form functional groups called nuclei Sensory & motor nuclei Gray matter is subdivided into regions called horns.
Anterior gray horn = motor nuclei for skeletal myo’s Posterior gray horn = somatic & autonomic sensory nuclei.
Lateral gray horn = autonomic motor nuclei for smooth myo, heart & glands (only in part of cord).
Spinal cord anatomy
White matter is organized into regions also —called columns.
Anterior white column Posterior white column Lateral white column Each column contains distinct bundles of axons going to & from the same place.
Ascending sensory tracts Descending motor tracts
Spinal nerve anatomy
Spinal nerves are part of PNS. Connect CNS to myo’s, glands, organs & receptors.
They are mixed nerves b/c they contain sensory & motor neurons from the roots that form them.
Spinal nerve anatomy
A “nerve” is a bundle of axons with their protective coverings.
Individual axons are wrapped in endoneurium.
Groups of these are arranged into fascicles, each wrapped in a perineurium.
The outermost covering on the entire nerve is called epineurium.
Contains many blood vessels to nourish nerve.
Spinal nerve anatomy
Immediately after exiting btwn the vertebrae, spinal nerves branch into ant. & post. rami.
Anterior rami of several spinal nerves can weave together to form a plexus.
Cervical Brachial Lumbar Sacral
Spinal nerve anatomy
A dermatome is an area of skin that provides sensory info to CNS via posterior roots of one spinal nerve.
Reflex Arc
Spinal cord helps to maintain homeostasis by integrating information for reflexes.
Reflex = fast, automatic, unplanned sequence of actions.
Several types: Spinal —knee jerk Cranial —eye tracking Somatic —involves contraction of skeletal myo’s Autonomic —responses of organs & glands
Reflex Arc
1.
2.
3.
4.
5.
Reflex arc has 5 components Sensory receptor —AP is generated in dendrites of this neuron.
Sensory neuron —impulse propagates along axon to gray matter of spinal cord or brain.
Integrating center —gray matter in CNS Motor neuron —AP travels down motor neuron to part of body that will respond.
Effector —part of body that responds.
Reflex Arc
Reflexes are predictable.
Can provide info about health of nervous system.
Reflex Arc
Stretch reflex is one example. It causes contraction of a skeletal myo that’s been stretched.
Slight stretch stimulates receptors in myo called muscle spindles.
Spindle generates AP along somatic sensory neuron thru posterior root of spinal nerve into spinal cord.
In cord, sensory neuron synapses with motor neuron in anterior gray horn.
Reflex Arc
AP begins in motor neuron which extends from spinal cord into anterior root back to the skeletal myo.
Neuron synapses on that myo & causes contraction.
At same time a small, interneuron is stimulated so that the opposing myo is inhibited.
Part 3: The Brain & Cranial Nerves
“Concepts” chapter 15 & 16
The Brain--overview
Adult brain has 4 main parts: Brain stem medulla oblongata, pons, midbrain Cerebellum Diencephalon thalamus, hypothalamus, epithalamus Cerebrum
The Brain -overview
Covered by cranial meninges which are continuous with spinal ones.
Internal carotid & vertebral arteries supply brain. Internal jugular vein drains it.
Needs constant supply of glucose for neurons to make ATP.
The Brain -overview
Blood brain barrier protects brain from harmful substances.
The capillaries are sealed tightly & astrocytes surround them as well.
The Brain -overview
Glucose, ions & some other small molecules can pass.
Lipid soluble substances (O 2 , CO 2 , alcohol & anesthetics) cross easily.
Many drugs do not.
The Brain -overview
Cerebrospinal fluid continuously circulates thru cavities in brain & spinal cord.
Contains glucose, proteins, lactic acid, urea, ions & WBC’s Provides shock absorbing protection, optimal chemical environment & exchange of nutrients & waste.
The Brain —brain stem
Medulla oblongata Most inferior part of brain stem Its white matter contains all sensory & motor tracts.
90% of the axons cross here (that’s why right side of brain controls left side of body).
The Brain —brain stem
Cardiovascular center is here Regulates rate & force of heart rate & diameter of blood vessels.
Respiratory center Adjusts basic breathing rhythm Monitors joint & myo position
The Brain —brain stem
Pons Just superior to medulla Has areas that help control breathing rhythm also.
Main “bridge” between parts of brain.
The Brain —brain stem
Midbrain Connects pons to diencephalon.
Has superior colliculi tracking —reflex center for eye Also inferior colliculi thalamus.
—relays auditory info to Both together allow for the startle reflex.
Some nuclei here control subconscious myo movement.
The Brain —brain stem
Also in brain stem is a less defined area called reticular formation.
Part of ret. form. is called reticular activating system (RAS).
Helps maintain consciousness especially when waking up.
The Brain--cerebellum
The Brain--cerebellum
Second largest part of brain (cerebrum is 1 st ).
Located posterior to medulla & pons & inferior to the post. portion of cerebrum.
Has 2 cerebellar hemispheres separated by the vermis.
Cortex is gray matter, interior “tree like” area is white matter.
The Brain--cerebellum
Inferior view of the Brain Stem and Cerebellum.
1. Pons 2. Medulla oblongata 3. Tonsilla cerebelli 4. Uvula 5. Pyramis 6. Tuber vermis 7. Biventer lobule 8. Inferior semilunar lobule 9. Vermis 10. Cerebellar hemisphere
The Brain--cerebellum
Receives sensory info from the vestibular apparatus (balance sensors) of inner ear & from proprioceptors (position sensors) thru out the body.
Cerebrum initiates movements, cerebellum evaluates how well they are being carried out.
The Brain--cerebellum
Function: Can correct movements & smooth them out.
Regulates posture & balance.
Helps coordinate myo’s for speech.
Also has nonmotor fxns.
Cognition & language processing
The Brain--diencephalon
Extends from brain stem to cerebrum.
Includes thalamus, hypothalamus & epithalamus.
The Brain--diencephalon
Thalamus Relays all sensory info to cerebral cortex Crude perception of pain, touch, pressure, temp.
Epithalamus Contains pineal gland which secretes melatonin.
Involved in sleep-wake cycle.
Involved in emotional response to odors
The Brain--diencephalon
Hypothalamus Controls & integrates autonomic nervous system (contraction of smooth & cardiac myo & gland secretions).
Produces many hormones.
Regulates behavior patterns (anger, pleasure, etc).
Regulates eating & thirst.
Monitors body temp.
Regulates sleep-wake cycle.
The Brain--diencephalon
The Brain--cerebrum
Called the “seat of intelligence.” Allows us to: Read Write Speak Calculate Compose Remember Plan Imagine
The Brain--cerebrum
Has right & left hemispheres separated by longitudinal fissure.
Outer rim of gray matter.
Inner cortex of white matter.
Some gray matter nuclei deep within white matter.
Has many folds called gyri (sing.--gyrus) with valleys called sulci (sing.--sulcus).
The Brain--cerebrum
Corpus callosum connects the hemispheres.
The Brain--cerebrum
Each hemisphere is divided into 4 lobes Frontal Parietal Temporal Occipital
The Brain--cerebrum
Central sulcus —separates frontal & parietal lobes.
Precentral gyrus —ant. to central sulcus, primary motor area Postcentral gyrus —post. to central sulcus, somatosensory area Lateral cerebral sulcus —separates frontal lobe from temporal.
Parieto-occipital sulcus —separates parietal lobe from occipital.
The Brain--cerebrum
1.
2.
3.
White matter consists of axons that form 3 types of tracts: Association —connect gyri in same hemisphere Commissural —connects gyri of different hemispheres Projection —to & from lower part of CNS
The Brain--cerebrum
Basal ganglia are the masses of gray matter within each cerebral hemisphere.
Coordinates gross, automatic myo movements (swinging arms while walking, etc.), & myo tone.
The basal ganglia consists of the
striatum
, the
globus pallidus
the
subthalamic nucleus
.
and
The Brain--cerebrum
Encircling upper brain stem & corpus callosum are a ring of structures that form the limbic system.
The Brain--cerebrum Limbic system is called “emotional brain.” Pain Pleasure Docility Affection Anger Smell & memory
The Brain--cerebrum
Cerebrum can be divided into
functional
areas: Sensory Motor Association
The Brain--cerebrum
Sensory This info arrives mostly in the post. half of both hemispheres.
Primary somatosensory area — receives nerve impulses for touch, joint/myo position, pain, temp, itch, tickle
The Brain--cerebrum
The Brain--cerebrum
Primary visual area — receives visual info.
Primary auditory area — receives info for sound & its perception.
Primary gustatory area — taste info & perception.
Primary olfactory area — smell & its perception.
The Brain--cerebrum
Motor Info from here flows mostly from anterior part of each hemisphere.
Primary motor area —controls voluntary myo contraction on opposite side of body.
Motor homunculus
The Brain--cerebrum
Broca’s speech area—involved in articulation of speech. Located in left hemisphere in most people.
Activates myo of larynx, pharynx, mouth & breathing.
The Brain--cerebrum
Association Consists of motor & sensory areas.
Somatosensory —permits you to determine size/shape of object w/out looking, compare current & previous experiences.
Frontal —connections w/ many areas, deals with make up of your personality, intelligence… Visual —recognize & evaluate what is seen Auditory —recognize sound/speech patterns
The Brain--cerebrum
Wernicke’s—in left hemisphere, involved in interpreting & recognizing speech.
Common integrative —receives info from many sensory areas, integrates them & formulates thoughts on them.
Premotor —deals with motor movements of complicated sequential nature Frontal eye field —voluntary scanning
The Brain--cerebrum
Brain structure on each side is nearly symmetrical.
There are functional differences. Some regions are lateralized more to one side.
The Brain--cerebrum
The Brain —cranial nerves
Twelve pairs Given their name b/c they exit the cranium thru various foramen.
Part of PNS.
Given a roman numeral which indicates their order from ant. post.
Also given a name that indicates their distribution or fxn.
The Brain —cranial nerves
Olfactory (I) nerve Sensory From nasal mucosa to olfactory area in cerebral cortex.
Fxn: smell
The Brain —cranial nerves
Optic (II) nerve Sensory From retina to thalamus & primary visual area.
Fxn: vision
The Brain —cranial nerves
Oculomotor (III) nerve Mixed Sensory portion: proprioceptors in eye myo’s to midbrain Motor portion: from midbrain to eye myo’s Fxn: proprioception, movement, lens & pupil
The Brain —cranial nerves
Trochlear (IV) nerve Mixed Sensory portion: proprioceptors in eye myo’s to midbrain Motor portion: midbrain to eye myo Fxn: proprioception & eye movement
The Brain —cranial nerves
Trigeminal (V) nerve Mixed Sensory portion: has 3 branches that receive info from many areas of face to pons Motor portion: pons to myo’s of mastication.
Fxn: pain, touch, temp. & proprioception, chewing
The Brain —cranial nerves
Abducens (VI) nerve Mixed Sensory portion: proprioceptors in eye myo’s to pons Motor portion: pons to eye myo’s Fxn: proprioception, eyeball movement
The Brain —cranial nerves
Facial (VII) nerve Mixed Sensory portion: tongue to cerebral cortex Motor portion: pons to facial myo’s, facial glands Fxn: proprioception, taste, facial expression, secretion of saliva & tears.
The Brain —cranial nerves
Vestibularcochlear (VIII) nerve Mixed Sensory portion: from receptors in inner ear to pons, cerebellum & cerebrum Motor portion: pons to hair cells in balance organ of inner ear.
Fxn: equilibrium & hearing
The Brain —cranial nerves
Glossopharyngeal (IX) nerve Mixed Sensory portion: from tongue & carotid arteries to medulla Motor portion: medulla to myo’s of tongue & larynx Fxn: taste, touch/pain, proprioception for swallowing, monitor O 2 CO 2 & & regulates breathing rate
The Brain —cranial nerves
Vagus (X) nerve Mixed Sensory portion: taste buds, myo of throat, receptors in aorta, receptors in organs to medulla & pons.
Motor portion: medulla to myo of throat & organs Fxn: taste, touch of throat, monitor blood pressure & breathing, organ sensation, swallowing, coughing, organ myo contraction.
The Brain —cranial nerves
Accessory (XI) nerve Mixed Sensory portion: proprioceptors in throat to medulla Motor portion: medulla & SC to throat & neck myo’s Fxn: proprioception, swallowing, head & shoulder movement
The Brain —cranial nerves
Hypoglossal (XII) nerve Mixed Sensory portion: proprioceptors in tongue to medulla Motor portion: medulla to tongue Fxn: proprioception, movement of tongue
Part 4: Autonomic Nervous System
“Concepts” chapter 17
Autonomic Nervous System
Recall that the cranial & spinal nerves discussed earlier are part of the somatic division of the PNS.
Somatic sensory neurons convey info about things like proprioception, pain, special sense… Somatic motor neurons stimulate skeletal myo’s to contract. They are under voluntary control (most).
Autonomic Nervous System
The main input into the ANS comes from autonomic sensory neurons.
Sensory receptors in blood vessels, organs & myo’s called interoceptors monitor internal conditions.
E.g. CO 2 in blood, amount of stretch in an organ This info gets conveyed to integrating centers in the CNS.
Autonomic Nervous System
Autonomic motor neurons regulate visceral activity by either increasing or decreasing activity in the effector tissue.
E.g. dilate blood vessels, increase heart rate, dilate pupils Remember that most somatic motor neurons went from CNS directly to skeletal myo. Autonomic motor pathways usually have 2 neurons.
Autonomic Nervous System
Myelinated axon from CNS autonomic ganglion (collection of nerve cell bodies) unmyelinated axon to the effector
Autonomic Nervous System
The (output) motor part of ANS has 2 types of functions. Sympathetic division Parasympathetic division The nerve impulse from a division will either increase or decrease activity in an effector.
E.g. impulses from sympathetic nerves to heart will speed it up, while impulses from parasympathetic nerves will slow it down.
Autonomic Nervous System
By the way… These autonomic fibers run right along with somatic fibers in the cranial & spinal nerves.
A “nerve” is made of a collection of neurons, some of which may be somatic & some may be autonomic types. Some neurons may be sensory & some motor.
Autonomic Nervous System
The preganglionic neurons of the
sympathetic
division have their cell bodies in the gray matter of the spinal cord in the thoracic & lumbar region.
So the sympathetic division is a.k.a thoracolumbar division.
Autonomic Nervous System
Preganglionic cell bodies of
parasympathetic
division originate in 4 cranial nerves, brain stem & sacral segments.
So it’s called craniosacral division.
Parasympathetic vs. sympathetic
ANS neurotransmitters & receptors Cholinergic neurons use acetylcholine (ACh) as a neurotransmitter.
All sympathetic & parasympathetic pre-gang neurons Sympathetic post-gang neurons to sweat glands All parasympathetic post-gang neurons Short lived effects
ANS neurotransmitters & receptors ACh will be released as a neurotransmitter via exocytosis from the neuron. It will bind to the post-ganglionic cell or effector cell membrane
if
there is a receptor for it.
Two main types of receptors & each triggers a different effect.
E.g. ACh can inhibit GI myo’s but excite myo’s that cause pupil contraction.
ANS neurotransmitters & receptors Adrenergic neurons release norepinephrine (NE) Most sympathetic post-gang neurons Adrenergic receptors bind both NE & epinephrine.
NE is a neurotransmitter & it can be released into blood by adrenal gland as a hormone.
Epinephrine is released as a hormone.
Longer effects
ANS
Most organs receive sympathetic & parasympathetic stimulation.
They usually work in opposition to each other.
The balance of each is called autonomic tone & is regulated by hypothalamus.
Sympathetic response
During physical or emotional stress, sympathetic division dominates.
Favors functions that support activity & production of ATP.
“E” situations: Exercise, emergency, excitement, embarrassment.
Fight or flight responses.
Parasympathetic response
Supports fxns that conserve & restore energy Rest & digest SLUDD Salivation Lacrimation Urination Digestion Defecation Decreases Heart rate, diameter of airway, diameter of pupil
Part 5: Endocrine System
“Concepts” chapter 19
Comparison of control
Nervous & endocrine systems act together to coordinate body functions and maintain homeostasis.
There are similarities and differences in how they do it.
Comparison of control
Nervous Endocrine
Mediator Neurotransmitter Distance to target cell Response Short Receptor on target cell?
Yes Fast Duration of response Short Hormone Usually far Yes Usually slow long
Endocrine system glands
Some glands can be “exocrine” type Secrete their product into a duct that opens into a body cavity Sweat, mucous, & digestive glands
Endocrine system glands
Some glands are “endocrine” type Secrete their products into a blood vessel so that it can be carried to the target
Glands & organs of the endocrine system
Mechanism of hormone action
Even though a hormone may travel in the blood stream and contact thousands of cells, not all of those cells will respond.
Cell must have a specific receptor for the hormone.
Mechanism of hormone action
Also, two cells may have a receptor for a hormone, but respond differently depending on the “machinery” inside.
Mechanism of hormone action
The binding of a hormone to a receptor will start a chain reaction response inside of a cell.
Mechanism of hormone action
Synergistic effect —when the effect of 2 hormones acting together is greater than each acting alone.
Epinephrine & glucagon both raise blood glucose levels Antagonistic effect —when one hormone opposes the action of another.
E.g. calcitonin & PTH
Hypothalamus
Called “master gland” Receives input from many areas of brain & internal organs Controls ANS, regulates body temp., thirst, hunger, sexual drive, fear, rage Crucial endocrine gland that secretes many hormones Works along with the pituitary gland
Hypothalamus
There are specialized neurons in the hypothalamus called neurosecretory cells.
They synthesize “stimulating” and “inhibiting” hormones in their cell bodies & package them in vesicles.
Nerve impulses cause exocytosis of the contents of these vesicles into the blood vessels that connect the hypothalamus & pituitary.
Pituitary then secretes the appropriate hormone to travel throughout the body.
Homeostasis
There are hundreds of body functions that need to be kept in balance.
Focus on the selected ones that follow
Homeostasis
Thyroid hormone balance is important for body metabolism
Homeostasis
Homeostasis
Homeostasis
Homeostasis —epinephrine & norepinephrine Secretion regulated by the nervous system in response to stress.
Raises blood glucose level and blood fatty acid level.
Increase metabolic activities.
Increases heart rate and stroke volume and dilates bronchioles.
Shunts blood away from skin, digestive organs, and kidneys, and increases blood flow to heart, brain, and skeletal muscle.
Homeostasis —glucocorticoids & mineralcorticoids Raises blood glucose level Causes kidney to excrete less water
The End