Chapter 12 Spinal Cord and Spinal Nerves

12-1

Spinal Meninges

• Connective tissue membranes surrounding spinal cord and brain –

Dura mater

: continuous with epineurium of the spinal nerves----thick –

Arachnoid mater

: thin and wispy –

Pia mater

: bound tightly to surface of brain and spinal cord. 12-2

Cross Section of Spinal Cord

•

Roots

: spinal nerves arise as rootlets then combine to form roots – Dorsal (posterior) root has a ganglion – Ventral (anterior) – Two roots merge laterally and form the spinal nerve 12-3

•

Organization of Neurons in the Spinal Cord and Spinal Nerves

Dorsal root ganglion

: collections of cell bodies of unipolar sensory neurons forming dorsal roots.

• Motor neuron cell bodies are in anterior and lateral horns of spinal cord gray matter. – – Multipolar somatic motor neurons in anterior (motor) horn Autonomic neurons in lateral horn • Axons of motor neurons form ventral roots and pass into spinal nerves 12-4

Reflex Arc

• Basic functional unit of nervous system and simplest portion capable of receiving a stimulus and producing a response • Automatic response to a stimulus that occurs without conscious thought. Homeostatic.

• Components – Action potentials produced in

sensory receptors

transmitted to –

Sensory neuron

. To-

Interneurons

. To-

Motor neuron

. To –

Effector organ

which responds with a

reflex

12-5

Structure of Peripheral Nerves

• Consist of – – – Axon bundles Schwann cells Connective tissue •

Endoneurium

: surrounds individual neurons •

Perineurium

: surrounds axon groups to form fascicles •

Epineurium

: surrounds the entire nerve 12-6

Branches of Spinal Nerves

•

Dorsal Ramus

: innervate deep muscles of the trunk responsible for movements of the vertebral column and the C.T. and skin near the midline of the back.

•

Ventral Ramus

: what they innervate depends upon which part of the spinal cord is considered.

– Thoracic region: form

intercostal nerves

muscles and the skin over the thorax that innervate the intercostal – Remaining spinal nerve ventral rami (

roots

(intermingling of nerves).

of the plexus): form five plexuses • Ventral rami of C1-C4=

cervical plexus

• Ventral rami of C5-T1=

brachial plexus

• Ventral rami of L1-L4=

lumbar plexus

• Ventral rami of L4-S4=

sacral plexus

• Ventral rami of S4 and S5=

coccygeal plexus

12-7

Chapter 13 Brain and Cranial Nerves

13-8

• •

Brain and Cranial Nerves

Brain

– Part of CNS contained in cranial cavity – – – Control center for many of body’s functions Much like a complex computer but more Parts of the brain •

Brainstem

: connects spinal cord to brain; integration of reflexes necessary for survival •

Cerebellum

: involved in control of locomotion, balance, posture • •

Diencephalon

:

thalamus

,

hypothalamus Cerebrum

: conscious thought, control

Cranial nerves

: part of PNS arise directly from brain. Two pairs arise from cerebrum; ten pairs arise from brainstem 13-9

Sagittal Section of Brain

13-10

13-11

Brainstem:

Medulla Oblongata

• Most inferior part • Continuous with spinal cord; has both ascending and descending nerve tracts • Regulates: heart rate, blood vessel diameter, respiration, swallowing, vomiting, hiccupping, coughing, and sneezing

Brainstem:

Pons

• Superior to the medulla oblongata – Sleep center – Respiratory center coordinates with center in medulla 13-12

Brainstem:

Midbrain

• Also called

mesencephalon

• Small and superior to pons –

Tectum

: four nuclei that form mounds on dorsal surface of midbrain.

Corpora quadrigemina

• Each separate part is a colliculus • Two

superior colliculi

involved in visual reflexes; receive information from inferior colliculi, eyes, skin, cerebrum • Two

inferior colliculi

involved in hearing 13-13

Reticular Formation

• Group of nuclei scattered throughout brainstem • Controls cyclic activities such as sleep wake cycle (maintains alertness) 13-14

Cerebellum

• • Attached to brainstem posterior to pons

Cerebellar peduncles

: fiber tracts that communicate with other parts of brain – – –

Superior

: to midbrain

Middle

: to pons

Inferior

: to medulla oblongata • Gray cortex and nuclei with white matter (tracts) between • Cortex folded in ridges called

folia

; white matter resembles a tree (

arbor vitae

) 13-15

Cerebellar Functions

• • •

Flocculonodular lobe

: balance and eye movements

Vermis

and medial portion of hemispheres: posture, locomotion, fine motor coordination leading to smooth, flowing movements

Lateral hemispheres

, major portion: works with cerebrum to plan, practice, learn complex movements 13-16

Diencephalon

• Located between brainstem and cerebrum • Components:

thalamus

,

subthalamus

,

epithalamus

,

hypothalamus

13-17

Thalamus

• Two lateral portions connected by the

intermediate mass

• Surrounded by

third ventricle

• Sensory information from spinal cord synapses here before projecting to cerebrum – Medial geniculate nucleus information : auditory –

Lateral geniculate nucleus

information : visual –

Ventral posterior nucleus

: most other types sensory information 13-18

Hypothalamus

• • • Most inferior portion of diencephalon

Mammilary bodies

surface; olfactory reflexes and emotional responses to odors : bulges on ventral

Infundibulum

: stalk extending from floor; connects hypothalamus to posterior pituitary gland. Controls endocrine system.

• Receives input from viscera, taste receptors, nipples, external genitalia, prefrontal cortex • Efferent fibers to brainstem, spinal cord (autonomic system), through infundibulum to posterior pituitary, and to cranial nerves controlling swallowing and shivering • Important in regulation of mood, emotion, sexual pleasure, satiation, rage, and fear 13-19

13-20

Cerebrum

• Largest portion of brain • Composed of right and left

hemispheres

each of which has the following lobes: frontal, parietal, occipital, temporal • Sulci and Fissures –

Longitudinal fissure

: separates the two hemispheres –

Lateral fissure

: separates temporal lobe from frontal and parietal lobes –

Central sulcus

: separates frontal and parietal lobes • Cortex: outer surface –

Gyri

are folds (increase surface area) –

Sulci

are depressions 13-21

Cerebrum, cont.

• • • • •

Central sulcus

: between the

precentral gyrus

motor cortex) and

postcentral gyrus

(primary (primary somatic sensory cortex)

Frontal lobe

: voluntary motor function, motivation, aggression, sense of smell, mood

Parietal lobe

: reception and evaluation of sensory information except smell, hearing, and vision

Occipital lobe

: reception and integration of visual input

Temporal lobe

: reception and evaluation for smell and hearing; memory, abstract thought, judgment. Insula is within.

13-22

Meninges

• Connective tissue membranes –

Dura mater

: superficial – –

Arachnoid mater Pia mater

: bound tightly to brain – Spaces • •

Subdural

: serous fluid

Subarachnoid

: CSF 13-23

Ventricles

• • • •

Lateral ventricles

: within cerebral hemispheres; separated by

septa pellucida Third ventricle

: within diencephalon

Interventricular foramina

join lateral ventricles with third

Fourth ventricle

: associated with pons and medulla oblongata. Connected to third ventricle by the

cerebral aqueduct

, continuous with the spinal cord.

13-24

Cerebrospinal Fluid (CSF)

• Similar to serum, but most protein removed • Bathes brain and spinal cord • • Protective cushion around CNS

Choroid plexuses

produce CSF which fills ventricles and other parts of brain and spinal cord – Composed of ependymal cells, their support tissue, and associated blood vessels –

Blood-cerebrospinal fluid barrier

• Endothelial cells of capillaries attached by tight junctions • Substances do not pass between cells • Substances must pass through cells • Makes the barrier very selective 13-25

Chapter 14 Integration of Nervous System Functions

14-26

Senses

• Means by which brain receives information about environment and body.

•

Sensation

(

perception

): conscious awareness of stimuli received by sensory receptors. • Steps to sensation – Stimuli originating either inside or outside of the body must be detected by sensory receptors and converted into action potentials, which are propagated to the CNS by nerves.

– Within the CNS, nerve tracts convey action potentials to the cerebral cortex and to other areas of the CNS.

– Action potentials reaching the cerebral cortex must be translated so the person can be aware of the stimulus.

14-27

Types of Senses

• •

General

: distributed over large part of body. Receptor generates an action potential called a generator potential that then travels to the brain. Called

primary receptors

.

–

Somatic

(information about the body and environment): touch, pressure, temperature, proprioception, pain –

Visceral

pressure (information about internal organs): pain and

Special senses

: smell, taste, sight, hearing, balance. 14-28

Types of Sensory Receptors

• • • • •

Mechanoreceptors

: compression, bending, stretching of cells. Touch, pressure, proprioception, hearing, and balance

Chemoreceptors

: chemicals become attached to receptors on their membranes. Smell and taste

Thermoreceptors

: respond to changes in temperature

Photoreceptors

: respond to light: vision

Nociceptors

: extreme mechanical, chemical, or thermal stimuli. Pain 14-29

Types of Receptors Based on Location

• • •

Exteroreceptors

: associated with skin

Visceroreceptors

: associated with organs

Proprioceptors

: associated with joints, tendons (proprioception is the sense of the orientation of one's limbs in space) 14-30

14-31

Sensory Nerve Endings in Skin

14-32

Free Nerve Endings

• Simplest, most common sensory receptor • Scattered through most of body; visceroceptors are of this type.

• Type responsible for temperature sensation – Cold: 10-15 times more numerous than warm – Warm – Pain: responds to extreme cold or heat 14-33

Merkel (Tactile) Disks

• Associated with dome-shaped mounds of thickened epidermis in hairy skin • Light touch and superficial pressure 14-34

Pacinian Corpuscles

• Deep cutaneous pressure; vibration • When associated with joints, involved in proprioception (proprioception is the sense of the orientation of one's limbs in space) 14-35

Meissner (Tactile) Corpuscles

• • • • • Two-point discrimination Ability to detect simultaneous stimulations at two points on the skin. Used to determined texture of objects.

Numerous and close together on tongue and fingertips Light touch & light pressure 14-36

Sensory and Association Areas of the Cerebral Cortex

• Sensory –

Primary somatic sensory cortex

(

general sensory area

): posterior to the central sulcus. Postcentral gyrus.

– – General sensory input: pain, pressure, temperature

Taste area

: inferior end of postcentral gyrus – –

Olfactory cortex

: inferior surface of frontal lobe

Primary auditory cortex

: superior part of temporal lobe –

Visual cortex

: occipital lobe • Association areas: process of recognition –

Somatic sensory

: posterior to – primary somatic sensory cortex

Visual association

: anterior to visual cortex: present visual information compared to past information 14-37

Referred Pain

• Referred: sensation in one region of body that is not source of stimulus. Organ pain usually referred to the skin. Both the organ and that region of the skin input to the same spinal segment and converge on the same ascending neurons.

14-38

Phantom and Chronic Pain

•

Phantom

: occurs in people who have appendage amputated or structure removed such as a tooth. Gate control theory of pain-- in uninjured limb, pressure and touch sensation inhibits pain (thus the success of massage in pain relief). These sensations are lost with amputations and thus their inhibitory effect.

14-39

Control of Skeletal Muscles

• • Motor system: maintains posture and balance; moves limbs, trunk, head, eyes; facial expression, speech.

• Reflexes: movements that occur without conscious thought

Voluntary movements

achieve a specific goal : consciously activated to • Two neurons: upper and lower –

Upper motor neurons

: directly or through interneurons connect to lower –

Lower motor neurons

: axons leave the CNS, extend through PNS to skeletal muscles. Cell bodies in anterior horns of spinal cord and in cranial nerve nuclei of brainstem 14-40

Motor Areas of the Cerebral Cortex

• • •

Precentral gyrus

(primary motor cortex, primary motor area): 30% of upper motor neurons. Another 30% in premotor area. Control

voluntary

movements, especially fine motor movements of hands

Premotor area

: anterior to primary motor cortex. Motor functions organized before initiation

Prefrontal area

: motivation, foresight to plan and initiate movements, emotional behavior, mood 14-41

Direct Pathways

• Control muscle tone and conscious fine, skilled movements in the face and distal limbs • Direct synapse of upper motor neurons of cerebral cortex with lower motor neurons in brainstem or spinal cord • Tracts –

Corticospinal

: direct control of movements below the head –

Corticobulbar

control of movements in head and neck : direct 14-42

Indirect Pathways

• Control conscious and unconscious muscle movements in trunk and proximal limbs.

• Synapse in some intermediate nucleus rather than directly with lower motor neurons.

• Tracts –

Rubrospinal

: upper neurons synapse in red nucleus. Similar to comparator function of cerebellum. Regulates fine motor control of muscles in distal part of upper limb.

–

Vestibulospinal

: influence neurons innervating extensor muscles in trunk and proximal portion of lower limbs; help maintain upright posture.

–

Reticulospinal

posture.

: maintenance of 14-43

Cerebellum

• Helps maintain muscle tone in postural muscles, helps control balance during movement, and coordinate eye movements 14-44

Cerebellar Comparator Function 1. The motor cortex sends action potentials to lower motor neurons in the spinal cord.

2. Action potentials from the motor cortex inform the cerebellum of the intended movement.

3. Lower motor neurons in the spinal cord send action potentials to skeletal muscles, causing them to contract.

4. Proprioceptive signals from the skeletal muscles and joints to the cerebellum convey information & cerebellum helps accomplish fine motor coordination of simple movements. It compares the intended movement with the actual movement and the result is smooth & coordinated movements.

(ex: touching your nose--------not rapid complex movements) 14-45

Speech

• • Area normally in left cerebral cortex

Wernicke's area

: sensory speech- understanding what is heard and thinking of what one will say.

• •

Broca's area

: motor speech- sending messages to the appropriate muscles to actually make the sounds.

• Sound is heard first in the 1 o association area, then information travels to Wernicke's area. Neuronal connections between Wernicke's area and Broca's area.

Aphasia

: absent or defective speech or language comprehension. Caused by lesion somewhere in the auditory/speech pathway.

14-46

Right and Left Cerebral Cortex

• Right: controls muscular activity in and receives sensory information from left side of body • Left: controls muscular activity in and receives sensory information from right side of body • Sensory information of both hemispheres shared through commissures: corpus callosum • Language, and possibly other functions like artistic activities, not shared equally – – Left: mathematics and speech Right: three-dimensional or spatial perception, recognition of faces, musical ability 14-47

Chapter 16 Autonomic Nervous System

16-48

Peripheral Nervous System

• Peripheral nerves contain both motor and sensory neurons • Among the motor neurons, some of these are somatic and innervate skeletal muscles while some are autonomic and innervate smooth muscle, cardiac muscle, and glands • Sensory neurons are not subdivided into somatic and autonomic since there is overlap in function; e.g., pain receptors can stimulate both somatic and autonomic reflexes 16-49

Somatic and Autonomic Nervous Systems

Somatic

• Skeletal muscle • Conscious and unconscious movement • Skeletal muscle contracts • One synapse • Acetylcholine • Receptor molecules: nicotinic

Autonomic

• Smooth and cardiac muscle and glands • Unconscious regulation • Target tissues stimulated or inhibited • Two synapses • Acetylcholine by

preganglionic neurons

and ACh or norepinephrine by

postganglionic neurons

• Receptor molecules: varies with synapse and neurotransmitter 16-50

16-51

Autonomic Nervous System

• Divided into

sympathetic

and

parasympathetic divisions

well as the

enteric nervous system

as • Sympathetic and parasympathetic divisions often supply the same organs but differ in a number of features • The enteric nervous system – Nerve plexuses within the wall of the digestive tract. – Contributions from: sensory neurons between digestive tract and CNS, ANS motor neurons between the CNS and the digestive tract, and enteric neurons confined within the plexuses – Functions • Stimulate/inhibit smooth muscle contraction • Stimulate/inhibit gland secretions • Detect changes in content of lumen • Interneurons connect sensory and motor aspects of enteric 16-52

16-53

Sympathetic (Thoracolumbar) Division

• Preganglionic cell bodies in lateral horns of spinal cord T1-L2: thoracolumbar • Preganglionic axons pass through ventral roots to

white rami communicantes

to the retroperitoneal

sympathetic chain ganglia

. 16-54

1.

2.

Routes of Sympathetic Axons

Spinal nerves

spinal nerves.

: preganglionic axons synapse (at the same or different level) with postganglionic neurons within the sympathetic chain. These postganglion neurons exit the ganglia through the gray rami communicantes and re-enter

Sympathetic nerves

: preganglionic axons synapse (at the same or different level) with postganglionic neurons, which exit the ganglia through sympathetic nerves 16-55

Routes of Sympathetic Axons

3.

4.

Splanchnic nerves

: preganglionic axons pass through the chain ganglia without synapsing to form splanchnic nerves. Preganglionic axons then synapse with postganglionic neurons in collateral ganglia. Postganglionic neurons then send fibers to target organs (viscera).

Innervation to adrenal gland

: preganglionic axons synapse with the cells of the adrenal medulla. Embryologically, adrenal medulla is derived from same cells as postganglionic ANS cells. Medullary cells secrete epinephrine and norepinephrine; act as hormones promoting physical activity.

16-56

Parasympathetic (Craniosacral) Division

• • Preganglionic cell bodies in nuclei of brainstem or lateral parts of spinal cord gray matter from S2-S4 – Preganglionic axons from brain pass to terminal ganglia through cranial nerves III, VII, IX and X – Preganglionic axons from sacral region pass through

pelvic splanchnic nerves

terminal ganglia to

Terminal ganglia

located near organ innervated or embedded in wall of organ 16-57

Enteric Nervous System

• Consists of nerve plexuses within wall of digestive tract – Sources of neurons • Sensory neurons that connect the digestive tract to CNS • ANS motor neurons that connect CNS to digestive tract • Enteric neurons that are confined to enteric plexuses 16-58

Parasympathetic Division

• 1.

Outflow is through cranial and pelvic splanchnic nerves a.

Cranial nerves supplying the head and neck. Preganglion axons extend to terminal ganglia in head. Postganglionic neurons supply nearby structures.

Oculomotor nerve through ciliary ganglion. Ciliary muscles and iris of the eye b.

c.

Facial nerve through pterygopalatine ganglion supplies lacrimal gland and mucosal glands of nasal cavity and palate. Through submandibular ganglion, supplies submandibular and sublingual salivary glands Glossopharyngeal nerve through otic ganglion supplies parotid salivary gland 16-59

Sensory Neurons in Autonomic Nerve Plexuses

• Parts of reflex arcs regulating organ activities • Transmit pain and pressure sensations from organs to the CNS 16-60

Physiology of ANS

• Neurotransmitters: primary substances produced by neurons of ANS –

Acetylcholine

released by

cholinergic neurons

–

Norepinephrine

released by

adrenergic neurons

• Certain cells have neurotransmitters causing a response in the cell –

Cholinergic receptors

that combine with : bind acetylcholine. Have two different forms:

nicotinic

and

muscarinic

• Nicotinic: all receptors on postganglionic neurons, all skeletal muscles, adrenal glands • Muscarinic: all receptors on parasympathetic effectors, receptors of some sweat glands –

Adrenergic receptors

• bind norepinephrine/epinephrine

Alpha

and

beta

categories. α β 2 1 receptors.These are further subdivided into and β 1 usually have opposite affects than α 2 and 16-61

Location of ANS Receptors

16-62

16-63

16-64

Regulation of ANS

• Autonomic reflexes control most of activity of visceral organs, glands, and blood vessels.

• Autonomic reflex activity influenced by hypothalamus and higher brain centers, but it is the hypothalamus that has overall control of the ANS.

• Sympathetic and parasympathetic divisions influence activities of enteric nervous system through autonomic reflexes. These involve the CNS. But, the enteric nervous system can function independently of CNS through local reflexes. E.g., when wall of digestive tract is stretched, sensory neurons send information to enteric plexus and then motor responses sent to smooth muscle of gut wall and the muscle contracts.

16-65

Autonomic Reflexes

a) Parasympathetic reflex via vagus lowers heart rate.

b) Sympathetic reflex via cardiac accelerator nerves (sympathetic) cause heart rate to increase.

16-66

Enteric Nervous System: Autonomic and Local Reflexes

• Regulation of activity of digestive tract • Sensory neurons of enteric plexuses supply CNS with information • • Autonomic neurons affect responses of smooth muscle and glands

Local reflex

: does not involve CNS. Produces involuntary, unconscious, stereotypical response to stimulus. E.g., stretch of wall of digestive tract causes contraction of smooth muscle of the wall.

16-67

Influence of Brain on Autonomic Functions

16-68

Functional Generalizations of ANS

• Dual innervation to most organs with sympathetic and parasympathetic having the opposite effects.

• Either division alone or both working together can coordinate activities of different structures.

• Sympathetic prepares body for physical activity or flight-or-fight response. But also important at rest. Blood vessel walls receive only sympathetic stimulation, so at rest, sympathetic is responsible for maintenance of blood pressure.

• In general, parasympathetic more important for resting conditions: SLUDD: salivation, lacrimation, urination, digestion, defecation 16-69

Innervation of Organs by ANS

16-70

Responses to Exercise (Fight or Flight Response)

• Increased heart rate and force of contraction • Blood vessel dilation in skeletal and cardiac muscles • Dilation of air passageways • Energy sources availability increased – – Glycogen to glucose Fat cells break down triglycerides • Muscles generate heat, body temperature increases • Sweat gland activity increases • Decrease in nonessential organ activities 16-71