Transcript 1 - Lone Star College System
Chapter 08 Lecture Outline
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8.1 Nervous System
2
A.
Functions
1.
2.
3.
Sensory input – sensory receptors respond to external and internal stimuli Integration – interpretation of sensory input Motor output – response by muscles, glands, and organs 3
B.
Divisions of the Nervous System
1.
2.
Central nervous system (CNS) a.
b.
a.
Peripheral nervous system (PNS) – includes all the cranial and spinal nerves Afferent (sensory) division – includes somatic and visceral divisions b.
Brain Spinal cord Efferent (motor) division – includes somatic and autonomic divisions 4
Organization of the Nervous System
5
C.
Nervous tissue
1.
a.
b.
Types of cells Neurons (nerve cells) – transmit impulses Neuroglia – support and nourish neurons 6
2.
Neuron (nerve cell) structure
a.
b.
c.
Cell body – contains nucleus and other organelles Dendrites – receive signals from sensory receptors or other neurons Axon 1) Conducts nerve signals away from cell body 2) 3) Nerve – bundle of parallel axons in the PNS Tract – bundle of parallel axons in the CNS 7
Neuron structure, cont
d.
1) Axon may be covered by the myelin sheath (lipid coating) Formed by Schwann cells or neurolemmocytes in PNS 2) 3) 4) 5) Formed by oligodendrocytes in CNS Provides insulation Increases the speed of impulse conduction Nodes of Ranvier – gaps in the myelin sheath 8
Neuron Anatomy
9
3.
Types of neurons
a.
b.
Motor neurons 1) Take nerve impulses from the CNS to muscles, organs, or glands 2) Multipolar – have many dendrites and a single axon Sensory neurons 1) Take nerve impulses from sensory receptors to the CNS 2) Almost all are unipolar 10
Types of neurons, cont
c.
1) 2) 3) 4) Interneurons (association neurons) All are in the CNS Typically multipolar Convey nerve impulses between various parts of the CNS Form complex pathways for thinking, memory, and language 11
D.
Nerve signal conduction
1.
Resting potential a.
b.
c.
d.
Neuron possesses potential energy The cell membrane is polarized 1) 2) Positively charged outside the cell due to sodium ions (Na + ) Negatively charged inside due to potassium ions (K + ) and large anions The membrane is impermeable to Na + but permeable to K + The sodium/potassium pump moves ions to maintain resting potential 12
a.
b.
c.
d.
e.
2.
Action potential
Process of conduction of nerve signals Occurs in the axons Begins with a stimulus Voltage-gated channels in the cell membrane open and sodium ions rush into the cell (depolarization); the membrane becomes negative outside and positive inside Sodium channels close and voltage-gated potassium channels open to allow K + to move out; the Na + /K + to their proper place and the cell repolarizes pump returns ions 13
Resting potential and action potential in an unmyelinated axon 14
3.
Conduction of action potentials (APs)
a.
b.
c.
d.
e.
As the axon depolarizes, Na+ will diffuse into the next section, causing depolarization Continues down the axon, followed by repolarization It is an all-or-none event Intensity of message determined by the rate of action potentials 1) Refractory period Axon cannot conduct an AP 2) Ensures one-way direction of an impulse 15
Conduction of action potentials (APs), cont f.
g.
In unmyelinated axons 1) 2) Slow (~1 meter/second) Each section of the axon must be stimulated In myelinated axons 1) Called saltatory conduction 2) 3) An AP at one node of Ranvier can “jump” over myelinated portion of axon to the next node Much faster (>100 meters/second) 16
Conduction of an action potential
17
E.
Transmission across a synapse
1.
2.
Axon terminal – small swelling at tips of the branched end of an axon Synapse components a.
Region of close proximity between two neurons b.
Presynaptic membrane – membrane of the first neuron c.
d.
Postsynaptic membrane – membrane of the next neuron Synaptic cleft – small gap between the presynaptic and the postsynaptic neuron 18
Transmission across a synapse, cont
3.
4.
a.
b.
c.
Neurotransmitters (NTs) – molecules stored in the axon terminal that transmit a nerve impulse across a synapse Information transfer Nerve impulse reaches axon terminal Calcium channels are opened and Ca 2+ enters the terminal Causes synaptic vesicles to fuse with the presynaptic membrane and release NT by exocytosis into synaptic cleft 19
d.
e.
f.
g.
Information transfer, cont
NT diffuses to postsynaptic membrane and binds to its specific receptor Ligand-regulated gates will open Depending on the NT, the postsynaptic membrane will be excited or inhibited The NT will be removed from the synapse so that further stimulation may occur 20
Synaptic structure and function
21
F.
Graded potentials and synaptic integration 1.
2.
3.
4.
Graded potentials – each small signal from a synapse Excitatory neurotransmitters produce a graded potential that promotes an AP; opens Na + gates inward Inhibitory neurotransmitters produce a graded potential that inhibits an AP; opens K + gates outward or Cl gates inward Integration involves summing up the excitatory and inhibitory signals 22
G.
Neurotransmitter molecules
1.
2.
3.
At least 75 have been identified Two well-known neurotransmitters a.
b.
Acetylcholine (ACh) Norepinephrine (NE) After a neurotransmitter has initiated a response it is removed from the synaptic cleft a.
b.
c.
Enzymes may inactivate the neurotransmitter The neurotransmitter may be reabsorbed by the presynaptic membrane Prevents continuous stimulation (or inhibition) of postsynaptic membranes 23
8.2 Central Nervous System
24
A.
Introduction
1.
2.
Gray matter – contains cell bodies and unmyelinated fibers White matter – contains myelinated axons 25
B.
Meninges and cerebrospinal fluid
1.
a.
b.
c.
Meninges – protective membranes of the CNS Dura mater – outer menix composed of two layers of tough, fibrous connective tissue; dural venous sinuses – spaces between the dura mater layers containing venous blood Arachnoid mater – middle menix composed of spider-web-like connective tissue Pia mater – deepest menix that adheres to the brain and spinal cord 26
Meninges
27
2.
Cerebrospinal fluid (CSF)
a.
b.
c.
d.
Produced from blood by the choroid plexus into the ventricles Fills the following: 1) Subarachnoid space – space between the arachnoid mater and the pia mater 2) Ventricles – hollow, interconnecting cavities of the brain 3) Central canal – hollow, space of the spinal cord Reabsorbed back into dural venous sinuses Blockages can occur that can cause hydrocephalus 28
Ventricles of the brain
29
C.
The spinal cord
1.
2.
Introduction a.
Extends from the foramen magnum to the first lumbar vertebra b.
c.
Protected by vertebral column Occupies the vertebral canal Spinal nerves – connect to the spinal cord through nerve roots through intervertebral foramen a.
Posterior (dorsal) root – carries sensory fibers into the spinal cord; posterior root ganglion b.
Anterior (ventral) root – carries motor fibers out of the spinal cord 30
3.
Structure of the spinal cord
a.
b.
c.
Central canal contains CSF Centrally located gray matter 1) 2) H-shaped Contains portions of sensory and motor neurons and interneurons White matter – surrounds gray matter 1) Posterior white matter composed of ascending tracts carrying sensory information to the brain 2) 3) Anterior white matter composed of descending tracts carrying motor information from the brain Tracts generally cross from one side of the spinal cord to the other 31
Spinal Cord
32
4.
Functions of the spinal cord
a.
b.
Provides communication between the brain and the peripheral nerves Reflex arcs 1) Sensory receptors respond to a stimulus 2) 3) Impulse travels over sensory neurons to the spinal cord Interneurons integrate data and relay a response by way of motor neurons 4) Motor neurons cause effectors to respond 33
A reflex arc
34
D.
The brain
1.
2.
3.
4.
5.
Cerebrum Diencephalon Cerebellum Brain stem a.
b.
c.
Ventricles Two lateral ventricles (cerebrum) Third ventricle (diencephalon) Fourth ventricle (brain stem and cerebellum) 35
The human brain
36
E.
The cerebrum
1.
Introduction a.
b.
c.
d.
Largest portion of the brain Receives sensory input, carries out integration, and initiates voluntary motor responses Coordinates the activities of the other parts of the brain Involved in higher thought processes 37
2.
Structure of the cerebrum
a.
b.
1) 2) Longitudinal fissure divides the cerebrum into left and right hemispheres Connected internally by the corpus callosum 3) Gyri (ridges) are separated by sulci (shallow grooves) Lobes 1) 2) 3) The cerebral hemispheres Frontal lobe Parietal lobes Temporal lobes 4) 5) Occipital lobe Insula 38
The lobes of a cerebral hemisphere
39
Structure of the cerebrum, cont
c.
d.
1) 2) Insula Deep to the lateral sulcus Functions may include speech processing, taste, and social emotions 1) Cerebral cortex Outer layers of gray matter 2) Accounts for sensation, voluntary movement, and consciousness 40
3.
Motor and sensory areas of the cortex a.
b.
Primary motor area 1) In frontal lobe anterior to central sulcus 2) 3) Each hemisphere controls voluntary commands to skeletal muscle of the opposite side of the body Cortex area related to the size of the motor units Primary somatosensory area 1) Posterior to central sulcus in parietal lobes 2) 3) Each hemisphere receives sensory information from the skin and skeletal muscles on the opposite side of the body Cortex area related to the number of receptors in an area 41
Body areas of primary motor and somatosensory areas of the cortex 42
Motor and sensory areas of the cortex, cont c.
d.
e.
Primary taste area 1) 2) Located in insula and parietal lobes Taste sensations Primary visual area 1) Located in the occipital lobe 2) Receives information from our eyes Primary auditory area 1) 2) Located in the temporal lobe Receives information from our inner ears 43
The lobes of a cerebral hemisphere
44
4.
Association areas
a.
b.
c.
Where integration occurs Where memories are stored Next to the primary area for the activity 45
5.
Processing centers
a.
b.
c.
d.
e.
Uses information from other association areas for higher level analytical functions Prefrontal area – reason and planning actions Premotor area – organizes motor functions for skilled movements Motor speech area (Broca’s area) Wernicke’s area (general interpretive area) – for written and spoken messages 46
6.
Central white matter
a.
b.
c.
d.
Tracts communicate information between the different sensory, motor, and association areas Tracts communicate with other brain areas Tracts communicate with the spinal cord 1) Descending tracts come from the primary motor area 2) Ascending tracts go to the primary somatosensory area Corpus callosum joins the two cerebral hemispheres 47
a.
b.
c.
7.
Basal nuclei
Masses of gray matter deep in the cerebrum Integrate motor commands Huntington disease and Parkinson’s disease – uncontrollable movements believed to be from neurotransmitter imbalances in the basal nuclei 48
F.
The diencephalon
1.
Hypothalamus a.
Forms the floor of the third ventricle b.
Integrating center involved in homeostasis c.
d.
e.
f.
Regulates hunger, sleep, thirst, body temperature, and water balance Link between nervous and endocrine systems Produces hormones released by the posterior pituitary gland Secretes hormones that control the anterior pituitary gland 49
The diencephalon, cont
2.
a.
b.
c.
d.
Thalamus Located in sides and roof of the third ventricle Functions as a sensory relay center for all sensory input except smell Involved in arousal of the cerebrum Participates in memory and emotions 3.
Pineal gland regulates body’s daily rhythms through the hormone melatonin 50
The human brain
51
G.
Limbic system
1.
2.
3.
4.
5.
Inferior to the cerebral cortex Contains neural pathways that connect portions of the cerebral cortex and the temporal lobes with the thalamus and the hypothalamus Causes emotion Involved in memory and learning Hippocampus involved in processing short term memory to become long-term memory 52
The Limbic System
53
H.
The cerebellum
1.
2.
3.
4.
5.
6.
Separated from brain stem by the fourth ventricle Two hemispheres composed primarily of internal white matter in a tree-like pattern Receives sensory input from the eyes, ears, joints, and muscles Receives motor output from the cerebral cortex Maintains posture and balance and ensures smooth, coordinated voluntary movement Assists in learning of new motor skills 54
I.
The brain stem
1.
2.
Midbrain a.
Relay station between cerebrum and the spinal cord or cerebellum b.
Pons a.
Contains bundles of axons traveling between the cerebellum and the rest of the CNS b.
c.
Reflex centers for visual, auditory, and tactile responses Helps regulate breathing rate with the medulla oblongata Reflex centers for head movements in response to visual and auditory stimuli 55
The brain stem, cont
3.
a.
b.
Medulla oblongata Vital reflex centers for heart rate, respiration, and blood pressure Reflex centers for vomiting, coughing, sneezing, hiccupping, and swallowing 56
a.
b.
c.
d.
e.
f.
4.
Reticular formation
Tracts and nuclei connected to many other brain areas Involved in maintaining muscle tone with the cerebellum Assists in regulating respiration, heart rate, and blood pressure with the medulla and pons Helps rouse a sleeping person with the thalamus Processes sensory stimuli to keep us mentally alert Damage may result in coma 57
The human brain
58
8.3 Peripheral Nervous System
59
A.
Introduction
1.
2.
3.
Lies outside of CNS Composed of nerves and ganglia Connective tissue components – endoneurium, perineurium, epineurium 60
4.
Subdivisions of the PNS
a.
b.
1) Afferent (sensory) Somatic sensory serves the skin, skeletal muscles, joints, and tendons; also special senses 2) 2) Visceral sensory serves the internal organs 1) Efferent (motor) Somatic motor system carries commands from CNS to the skeletal muscles Autonomic motor system regulates cardiac and smooth muscle and glands 61
1.
2.
3.
4.
5.
6.
B.
Cranial nerves
Twelve named pairs Sensory nerves contain only sensory fibers (nerves I, II, and VIII) Motor nerves contain only motor fibers (nerves III, IV, VI, XI, and XII) Mixed nerves contain both sensory and motor fibers (nerves V, VII, IX, and X) Mostly involved with the head, neck, and facial regions of the body The vagus nerve (cranial nerve X) has sensory and motor branches to the face and most of the internal organs 62
Cranial Nerves
63
Cranial Nerves
64
C.
Spinal nerves
1.
2.
3.
a.
31 pairs Designated according to their location in relation to the vertebrae Spinal nerves are mixed nerves Sensory fibers enter at the posterior root b.
c.
d.
Motor fibers exit at the anterior root The cell body of a sensory neuron is in a posterior-root ganglion The cell body of a motor neuron is in the anterior gray matter of the cord 65
Spinal Nerves
66
Spinal Nerves
67
D.
Somatic motor nervous system and reflexes 1.
2.
3.
Includes voluntary actions that originate in the motor cortex a.
Reflexes are automatic involuntary responses to changes inside and outside the body Cranial reflexes involve the brain b.
Spinal reflex involves only the spinal cord Imbalances in reflexes can be used to determine if the nervous system is reacting properly, can help avoid injury, and help maintain balance 68
Reflex arc showing spinal reflex
69
E.
Autonomic Nervous System (ANS)
1.
2.
a.
b.
Two divisions of ANS that: Function automatically and involuntarily Innervate all internal organs with fibers from either or both divisions c.
Utilize two motor neurons (preganglionic neuron and postganglionic neuron) and one ganglion for each impulse Visceral reflexes are important to the maintenance of homeostasis 70
3.
Sympathetic division of ANS
a.
b.
c.
d.
e.
f.
Called the “Fight or Flight” division that prepares the body for emergency situations Preganglionic fibers arise from the thoracic lumbar portion of the spinal cord Preganglionic fibers are short and postganglionic fibers are long The ganglia are near the spinal cord Neurotransmitter released by the postganglionic neuron is primarily norepinephrine (NE) Examples of functions - accelerates heartbeat and dilates the bronchi; inhibits the digestive tract 71
4.
Parasympathetic division of ANS
a.
b.
c.
d.
e.
f.
Called the “Rest and Digest” division that controls normal body activities Includes several cranial nerves and preganglionic fibers that arise from the sacral portion of the spinal cord (craniosacral portion of ANS) Preganglionic fiber is long and postganglionic fiber is short Ganglia are near or in the effectors Acetylcholine (Ach) is the neurotransmitter Examples of functions - promotes digestion of food, slows heart rate, and decreases the strength of cardiac contraction 72
Comparison of ANS Divisions
Sympathetic division neurons and ganglion Parasympathetic division neurons and ganglion 73
ANS structure and function
74
Autonomic Motor Pathways
75
8.4 Effects of Aging
76
Effects of Aging
A.
B.
C.
D.
E.
Brain mass decreases, particularly from the cerebral cortex Learning, memory, and reasoning decline Neurotransmitter production decreases Although structural changes occur, mental impairment is not an automatic consequence of getting older Neurological disorders are more likely to occur – Alzheimer disease, Parkinson’s disease 77
Effects of Aging, cont
F.
1.
2.
3.
4.
To help maintain good mental health: Maintain cardiovascular system health Do activities to stay mentally alert Avoid depression Exercise 78
8.5 Homeostasis
79
A.
B.
C.
Homeostasis of the nervous system
D.
Detects, interprets, and responds to changes in the internal and external environment With the endocrine system, it coordinates and regulates the functioning of other systems The hypothalamus and medulla oblongata control vital functions Controls body movements 80
Human Systems Work Together
81