Organization of Nervous System and the Spinal Cord

Structure of Peripheral Nerves

A nerve contains the axons of multitudes of individual neurons. Spinal nerves are MIXED NERVES: they contain both efferent and afferent neurons which branch at later points.

What is a sympathetic trunk?

Chain of ganglia (collection of cell bodies), lateral to spinal cord. (along the sides of the ganglia) Communicating rami connect spinal nerves to sympathetic trunks

Spinal nerves and spinal cord

31 pairs of spinal nerves )dorsal and ventral roots come together) Innervate neck, trunk, upper and lower limbs. Grouped by level they arise along numbered sequence: 1) Cervical Nerves: C1-C8 2) Thoracic Nerves: T1-T12 3) Lumbar Nerves: L1-L5 4) Sacral Nerves: S1-S5 5) Coccygeal Nerve: Co Most exit vertebral column via intervertebral foramina.

Dorsal root ganglion

A bulge in the dorsal root. GANGLIA: collection of cell bodies in PNS - all the cell bodies of sensory neurons are in ganglia

5 Step reflex arc

1) Arrival of stimulus and activation of receptor 2) Activation of sensory neuron 3) travels down dorsal root. Synapses on a neuron in the dorsal horn. Information processing in the CNS. 4) Activation of motor neuron 5) Response by effector This response will occur before the signal reaches our brain, before we are consciously aware we touched a tack.

4 Nerve Plexuses

1) Cervical plexus: - C1-C4 - Nerve supply to muscles/skin of the neck and the diaphragm. (causes contractions of diaphragm) 2) Brachial Plexus: - C5-T1 - Deep within shoulders - Nerve supply to muscle/skin of arm 3) Lumbar Plexus: - T12-L4 - Nerve supply to muscles/skin of the abdomen, external genitalia, hip thigh 4) Sacral Plexus: - L4-S2 - Nerve supply to muscles/skin of the butt, perineum, lower leg.

Meninges structure from out to in

1) Epidural space: Between the vertebrae and dura mater. Areolar and adipose tissue 2) Dura mater: Outer layer, dense collagen fibers longitudinally along the spinal cord 3) Arachnoid mater: Thin epithelial membrane, connected to SUBARACHNOID SPACE 4) Subarachnoid space - delicate connective tissue trabeculae and intercommunicating channels containing cerebrospinal fluid (CSF) - contains CSF 5) Pia mater: Inner layer, collagen and elastin. Sits directly on top of the spinal cord

Sensory Commands GO OVER Thoracic and upper lumbar region only

1) Sympathetic nerve carries sensory information from the visceral organs. - sensory information that was picked up by interoreceptors. 2) The ventral ramus carries sensory information from the ventrolateral body surfaces and limbs. 3) Dorsal ramus carries sensory information from the back. 4) The dorsal root carries sensory information (from both Ventral and Dorsal Ramus) to the spinal cord. 5) Somatic nuclei - proprioception Visceral nuclei - interoreceptors

Functions of Spinal Cord and Nerves

1) Transmission of sensory information to the brain (AFFERENT) 2) Transmission of motor information to from the brain (EFFERENT) 3) Generation of spinal reflexes 4) Spinal cord can take over walking 5) Spinal cord helps with maintenance of posture.

How many pairs of roots?

31 pairs of roots

Motor Commands from spinal cord GO OVER

A spinal nerve distributes motor commands that originate in motor nuclei of the thoracic or superior lumbar segments of the spinal cord. 1) The VENTRAL ROOT of each spinal nerve contains the axons of somatic motor and visceral motor neurons. 2) The spinal nerve forms just lateral to the intervertebral foramen, where the dorsal and ventral roots unite. 3) The DORSAL RAMUS contains somatic motor and visceral motor fibers for the back. 4) The VENTRAL RAMUS supply nerves to the front of the body. 5) The WHITE RAMUS... is the FIRST BRANCH from the spinal nerve and carries VISCERAL MOTOR fibers to a sympathetic ganglion. preganglionic 6) The GRAY RAMUS... contains postganglionic fibers that innervate glands and smooth muscles. Unmyelinated = gray WHITE AND GRAY RAMI ARE COMMUNICATING RAMI because they take info to and from sympathetic ganglion.

PNS

All nervous tissue outside of CNS Nerves: transmit information to and from the CNS. - bundles of axons

Dermatomes

Area of skin innervated by nerve fibers of a particular pair of spinal nerves. Shingles: a variant of the chicken pox virus - attacks neurons within the dorsal root ganglion of spinal nerves. - painful rash and blistering - follows the dermatome of affected spinal nerve.

What is the central canal

Cerebrospinal fluid travels through the central canal.

CNS

Brain Spinal cord

What are tracts?

Bundles of white axons with similar structure and function. They relay info up and down the spinal cord.

Commissures?

Commissures are both white and gray. They are axons that CROSS SIDES Because of this, right side of brain controls the left side.

Nerve Plexuses

Complex networks of nerves formed by ventral rami of spinal nerves. Ventral rami of different spinal nerves intermingle A branching network of intersecting nerves. VENTRAL ONLY - ventral rami covers more area, does more stuff.

Communicating Rami

Connect spinal nerves to SYMPATHETIC TRUNKS. - WHITE RAMUS (myelinated): thoracic, T1-L2 only - GRAY RAMUS (unmyelinated): all spinal nerves

Cranial and Spinal nerves

Cranial nerves arise from the brain - 12 pairs Spinal nerves arise from the spinal cord - 31 pairs

The spinal nerve has branches. Two main branches.

Dorsal ramus, ventral ramus. Dorsal = innervates back - mixed information - smaller ventral ramus = - wraps around the front/arm/leg - mixed information

Nerve plexuses

Each network is a network of nerves that come together and then redistribute themselves out with a different distribution of nerves into the limbs. They are made from the rest of the ventral rami. Each end of each plexus contains fibers from several spinal nerves. The fibers from each ventral ramus travels along different routes so that each limb muscle receives innervation from more than 1 spinal nerve to have a backup plan in case of injury.

Epidural anesthesia/Spinal taps

Epidural anesthesia: - administration of anesthetics to the EPIDURAL SPACE within the LUMBAr region of the spine. - Pain reducing effect only on the nerves in that area. Lumbar puncture/Spinal Tap: - Sampling of CSF - Reducing CSF pressure - Site: SUBARACHNOID space tithing the lumbar region of vertebral column. - because in the subarachnoid space has CSF.

Layers of nerve

Epineurium: outer layer of dense connective tissue. Surrounds every nerve. Perineurium: surrounds fascicle - Fascicle: bundles of axons (thousands) - within an individual fascicle, we can have axons that are sensory and axons that are motor. Endoneurium: - surrounds individual nerve/axon cells

Crossed Extensor Reflex

Extension of opposite limb. Activation of sensory neuron - You will pick up you for when you step on a tack. - So there needs to be stimulation of excitatory motor neurons to extensor muscle on opposite limb (make sure you don't fall over when you pick up your foot) -There also needs to be stimulation of inhibitory interneurons to flexor on the opposite limb (make sure you don't flex your leg and lift it up while your other leg is in the air) This is a CONTRALATERAL reflex arc (crosses to the other side of the body) - axons cross the midline - commissures are axons that cross the midline

Meninges

Function: Provide structural support, shock absorption, house blood vessels

Withdrawal reflex: Polysynaptic reflex

Functions to remove body part from a painful stimulus. Receptor: nociceptor in skin on sensory neurons, which conduct action potentials through dorsal root on spinal cord. Interneurons: within the gray matter spinal cord. Communicate with flexor and extensor. EXCITE motor neurons to FLEXORS - increase firings of APs INHIBIT motor neurons to extensors - decrease firing of APs.

Gray matter vs White matter

Gray = horizontal communication White = columns, vertical info

Organization of gray matter

Gray matter: - organized into NUCLEI - DORSAL HORNS: somatic and visceral sensory nuclei, process/relay sensory information. - VENTRAL HORNS: somatic motor nuclei, integrates/relays motor information - LATERAL HORNS: (thoracic and lumbar only) visceral motor nuclei. - sympathetic motor system (relay visceral motor info)

Posterior median sulcus vs Anterior median fissure

Groove vs larger gap

Where are cell bodies of neurons found?

In the horns of the spinal cord, within the nuclei

Meningitis

Inflammation of the meninges Disrupts the flow of CSF - more waste, less nutrients, and pressure affects neurons Damages neurons in affected areas

Cross section of spinal cord

Inner GRAY matter: abundance of cell bodies/dendrites Outer WHITE matter: abundance of myelinated (and unmyelinated) axons. VENTRAL ROOTS: EFFERENT pathways - carry motor information away from the CNS to peripheral targets DORSAL ROOTS: AFFERENT pathways - Carry sensory information from periphery and towards the CNS. - DORSAL ROOT GANGILON: DGR - CELL BODIES of sensory neurons

How is white matter organized?

Into COLUMNS

Spinal Reflexes

Rapid, uncurious responses to specific stimuli - we have come innate reflexes - suckling - reflexes can be learned - reflexes are programmed and once activated reliably produce the same response - fast response

Patellar Reflex Monosynaptic Stretch Reflex

Receptor: muscle spindle (proprioceptor) Sensory neuron: stretch activates sensory neurons that innervate muscle spindle. Motor neuron: sensory neuron directly synapses with motor neuron in the spinal cord. Effector: muscle fibers in the region of spindle contract in response to action potentials from motor neurons. No interneurons involved

Nerve Plexus Definition

Some ventral rami merge with adjacent ventral rami to form a nerve plexus, a network of interconnecting nerves. Nerves emerging from a plexus contain fibers from various spinal nerves, which are now carried together to some target location. Major plexuses include the cervical, brachial, lumbar, and sacral plexuses.

Organization of Nervous system

Special sensory neurons: - smell taste vision, hearing, balance - Somatic Sensory neurons - skin, skeletal muscle, joints - outside of the body - Visceral Sensory neurons: INTERORECEPTORS - internal organs These sensory nerves go to the CNS and are processed, then motor neurons are signaled in either the..... - Somatic Nervous system - skeletal muscle contraction -Autonomic Nervous system - Smooth/cardiac muscle, glands, adipose The autonomic nervous system is divided into two categories: 1) Sympathetic Nervous system - STRESS response 2) Parasympathetic nervous system - REST response

Anatomy of Spinal Cord

Spinal cord exits at foramen magnum and extends through vertebral canal. Spinal cord in adult ENDS at level of the 1st LUMBAR VERTEBRAE - CERVICAL ENLARGEMENT: supplies nerves to the ARMS - LUMBAR ENLARGEMENT: supplies nerves to the LEGS - CONUS MEDULLARIS: tapering of spinal cord below the lumbar enlargement - FELIM TERMINALE: connective tissue that connects conus to coccygeal ligament. - NOT NERVOUS TISSUE The Cauda equnia is a bundle of nerve roots and felim terminal within vertebral canal from L2 to S5. The spinal cord is 18 inches long

Branches (Rami) of Spinal Nerves

Spinal nerve branches: - Dorsal Branch (ramus) of spinal nerve: - (small) - innervates narrow strip of muscles, joints, skin towards the back. - it is small because the spinal cord is already in the back. - Ventral Branch (ramus) of spinal cord: - (large) - innervates lateral and anterior trunk and limbs. The dorsal ramus and sensory ramus carry mixed information (both sensory and motor information) Every spinal nerve has a dorsal and ventral rams.

Information is mixed on a spinal nerve

The dorsal root and ventral root join together to make the spinal nerve, which carries mixed information.

Where does the spinal cord end?

The spinal cord stops at L1 but nerve roots continue.

Where are there no Nerves plexuses?

There are no nerve plexuses in THORACIC SPINAL NERVE. For all but, thoracic spinal nerves, the ventral rami of adjacent spinal nerves can interconnect via nerve plexuses.

Tricks

Thoracic Nerve: T1-T12 - T for thoracic T for twelve

We have 31 pair spinal roots

Ventral root (motor) and dorsal root (sensory) make up a pair.

Ventral vs Dorsal root

Ventral: anterior - closer to belly Dorsal: posterior - closer to back

White vs gray ramus

White - myelinated axons Gray - unmyelinated Every spinal nerve has a gray ramus. Only T1-L2 has white ramus

White vs Gray Rami function

White = carry signal to sympathetic ganglion Gray = carry signal away from sympathetic ganglion

Organization of White matter

White matter: - organized into COLUMNS - There are anterior, posterior and lateral columns. - Each column contains TRACTS - TRACTS: bundles of axons with similar structure and function. They relay information up and down spinal cord.

White vs Gray Rami

White rami communicantes carry preganglionic sympathetic fibers from the spinal nerves to the sympathetic ganglia. Gray rami communicantes carry postganglionic sympathetic fibers from the sympathetic ganglia to the spinal nerves. They are both COMMUNICATING RAMI????? ASK

White vs Gray

White: axons Gray: bodies/dendrites White matter is specialized for VERTICAL communication - towards and away from brain Gray matter is specialized for HORIZONTAL communication - via spinal nerves

Isolateral

Withdrawal, patellar Happens on same side of body.

Are spinal nerves paired?

YES

What is a nucleus

cell bodies in CNS

Nucleus vs Ganglia

cell bodies in CNS vs cell bodies in PNS