Spinal Cord and Nerves

The Nervous System

Coordinates the activity of muscles, organs, senses, and actions

Made up of nervous tissue Has 3 main functions:

1. Receives sensory Input 2. Integration 3. Dictates motor output

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Divisions of the Nervous System

Central Nervous System (CNS) Brain and spinal cord Interprets incoming sensory signals Dictates motor responses

Peripheral Nervous System (PNS) Ganglia Nerves

Cranial nerves and spinal nerves Communication between regions of

body and CNS pg 16

Review of Nervous Cells

Neuron Cell body Dendrite Axon

Myelin Sheath

Neuroglia Interneuron

Reflex Arc Synapse

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Organization of a Nerve Endoneurium

Surrounds each axon (nerve fiber) Myelinated and Unmyelinated axons Motor and Sensory nerve fibers Loose CT

Perineurium Bundles axons into fascicles CT

Epineurium Bundles fascicles into a nerve Fibrous CT

CT layers contain blood vessels

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Types of Nerve Signals/Fibers

Sensory (afferent) Picked up by sensory receptors thru body Carried by nerve fibers of PNS into CNS

Motor (efferent) Carried away from the CNS by nerve fibers

into PNS Innervate muscles and glands Causes these organs to contract or secrete

Remember: SAME

Sensory and Motor Signals/Fibers Somatic sensory

Body senses touch, pressure, temperature, vibration of body, muscles

stretching, balance Visceral sensory

Organ senses Stretch, pain, temperature in organs (eg) nausea, hunger, cramps

Somatic motor Body movement Voluntary contraction of skeletal muscles

Visceral motor Organ movement Contraction of smooth muscle, glands = Autonomic Nervous System (involuntary)

CNSBrain

Spinal cord

PNSCranial nerves and spinal nerves

Sensory (afferent)division

Motor (efferent)division

Somatic sensory

General: Touch, pain, pressure, vibration

Special: hearing, equilibrium, vision, smell

Visceral sensory

General: Stretch, pain, temperature, nausea, hunger

Special: Taste

Somatic motor

General: Motor innervation of all skeletal muscles

Visceral motor

General: Motor innervation of smooth muscle, cardiac muscle, and glands; = ANS

Parasympathetic division

Sympathetic division

CNS – Spinal Cord

Runs through vertebral canal of the vertebral column Protected by bone, meninges, and cerebrospinal fluid Spinal cord made of a core of gray matter surrounded

by white matter 31 pairs of spinal nerves branch off spinal cord through

intervertebral foramen Functions in many ways:

Involved in sensory and motor innervation of body inferior to the head (through spinal nerves)

Provides a 2-way conduction pathway for signals between body and brain

Major center for reflexespg 63

Meninges of Spinal Cord

Membranes surrounding the spinal cord 3 Layers of connective tissue Functions

Protect spinal cord Contains cerebrospinal fluid Protect blood vessels serving spinal cord

Meninges of Spinal Cord

Dura mater (superficial) Spinal dural sheath Does not attach to bone

Epidural space Fat and veins Between dura mater and vertebra

Subdural space Between dura mater and arachnoid

pg 67

Meninges of Spinal Cord

Arachnoid mater (middle) Impermeable layer = barrier Raised off pia mater by rootlets

Subarachnoid space Between arachnoid and pia mater Contains CSF

Pia mater (deep) Highly vascular Adheres to brain/spinal cord tissue

pg 67

Regions of Spinal Cord

Cervical Thoracic Lumbar Sacral Coccygeal Cervical + Lumbar enlargements Cauda equina Conus medullaris Filum terminale

CT & pia mater Attaches to coccyx

pg 63pg 24

Gray Mater

Consists of neuron cell bodies, unmyelinated axons, dendrites, and neuroglia

Shaped like an “H” Gray commissure (crossbar) Central canal

Posterior horns Anterior horns

pg 63

Gray Mater

Posterior horns Consist of interneurons that transmit in from outside spinal cord

into it Dorsal root contain sensory fibers

Somatic Sensory (SS) Visceral Sensory (VS)

Dorsal root ganglia - swelling in dorsal root that these interneurons pass through

Anterior horns Cell bodies of motor neurons send info out of spinal cord to

muscles and glands Ventral Root contains Motor Fibers

Visceral Motor Somatic Motor pg 63

White Mater

Surrounds gray matter Composed of myelinated and unmyelinated axons Divided into white columns (funiculi)

Posterior funiculus Anterior funiculus Lateral funiculus

Allow for communication between Parts of the spinal cord Spinal cord and brain

pg 63

White Mater 3 types of nerve fibers:

Ascending Carry sensory info from sensory neurons of body to brain touch, pressure, pain, temperature

Descending Carry motor instructions from brain to spinal cord Contraction of muscles and secretion of glands control precise, skilled movement = writing, maintain

balance, create movement Commissural

Cross from one side of cord to the other

Spinal Nerves (31 Pairs)

Part of the PNS (Somatic) Lie in intervertebral foramina

Send lateral branches to body Named according to their point of issue from the vertebral column

8 pairs of cervical spinal nerves; C1-C8

12 pairs of thoracic spinal nerves; T1-T12

5 pairs of lumbar spinal nerves; L1-L5

5 pairs of sacral spinal nerves; S1-S5

1 pair of coccygeal spinal nerves; C01

pg 71-2

Spinal Nerves

Each spinal nerve connected to spinal cord via dorsal (sensory) and ventral (motor) root

Spinal nerves branch into dorsal ramus and ventral ramus Ventral ramus

Connects to rami communicans, which then lead to sympathetic chain ganglia

Supply anterior and lateral regions of the neck, trunk, and limbs

Dorsal ramus Supply the dorsum of the neck and

trunk (back) pg 81

The Big Picture

Just lateral to intervertebral foramen, each spinal nerve then splits in 2

Dorsal Rami Ventral Rami

Contain BOTH Sensory and Motor fibers!!

pg 68

CNSBrain

Spinal cord

PNSCranial nerves and spinal nerves

Sensory (afferent)division

Motor (efferent)division

Somatic sensory

General: Touch, pain, pressure, vibration

Special: hearing, equilibrium, vision, smell

Visceral sensory

General: Stretch, pain, temperature, nausea, hunger

Special: Taste

Somatic motor

General: Motor innervation of all skeletal muscles

Visceral motor

General: Motor innervation of smooth muscle, cardiac muscle, and glands; = ANS

Parasympathetic division

Sympathetic division

Autonomic Nervous System = Visceral Motor

Autonomic Nervous System

Visceral Motor Function Not easily controlled by will

Get nervous and sweat Innervate smooth muscle, cardiac muscle,

glands Regulate visceral function

Heart rate, blood pressure, digestion, urination Has 2 divisions:

Parasympathetic Sympathetic

Autonomic Nervous System

Parasympathetic “rest and digest” Enables body to

unwind and calm down Most active when body

at rest Routine maintenance

functions Craniosacral division

Fibers emerge from brain and sacral spinal cord

Sympathetic “fight or flight” Mobilizes the body

during extreme situations

Becomes active when extra metabolic effort needed

Thoracolumbar division

Fibers arise from thoracic and lumbar parts of spinal cord

Somatic Nervous System

Innervates skeletal muscle Neurons runs from CNS directly to muscle Consists of single neuron plus skeletal

muscle cells Voluntary control

Running, moving limbs, typing on a computer!