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

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

PNS

Somatic

ANS Sympathetic

Parasymp.

Enteric

CNS

PNS

Nervous system structures outside the brain and spinal cord

Either somatic or visceral Visceral motor portion is the ANS

Structural components: Sensory receptors Motor endings Nerves and ganglia

PNS - Nervous Tissue

Made up of 2 cells: Neurons

Conduct electrical impulses

Supporting cells Surround the

neurons Ex. Glial cells

The Neuron

Nerve cells Transmit signals in form of

nerve impulses Have extreme longevity Do not divide High metabolic rate

Neuronal Anatomy

Cell body (soma) Most are in CNS

Neuron processes Dendrites

Toward cell body Axons

Transmit away from cell body

Synapses Site where neurons

communicate

Neuronal Anatomy

Myelin sheath Fatty sheath that surrounds most nerve fibers

Reflex arc Responses to a stimulus

Interneuron Nerve cell that lies between a sensory neuron

and motor neuron in a reflex arc Confined entirely within the CNS

PNS - Sensory and Motor Signals

Divided by the body regions they serve:

Sensory division Somatic sensory Visceral sensory

Motor division Somatic motor Visceral motor

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)

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

Spinal Cord Segments

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 communicates, 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)

Roots V. Rami

Rami Lateral branches of

spinal nerves Each contains both

sensory fibers and motor fibers

Roots Lie medial to the spinal

nerves Strictly sensory

(dorsal) or motor (ventral)

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!!

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

ANS

Parasympathetic 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

ANS Includes a chain of 2 motor neurons

Preganglionic neuron Preganglionic axon

Ganglionic neuron Postganglionic axon

Autonomic neuron synapses 2 neurons

PNS

Somatic NS Autonomic NS

Sympathetic division Parasympathetic

division Enteric division

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!

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 reflexes

Spinal Cord Growth

Until 3rd month of development, does not run to coccyx

As vertebral column grows caudally, spinal cord becomes more rostral

At birth, ends at L3

During childhood, terminates at L1 and L2

Adults runs from medulla oblongata to L1

Regions of the Spinal Cord

Cervical Thoracic Lumbar Sacral Coccygeal Cervical + Lumbar

enlargements Cauda equina Conus medullaris Filum terminale

Meninges of Brain and 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

Meninges of Brain and 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

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

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

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

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

Nervous System Overview