The Nervous System The Spinal Cord-part of the CNS found within the spinal column The spinal cord communicates with the sense organs and muscles below

The Nervous System

The Spinal Cord-part of the CNS found within the spinal column

The spinal cord communicates with the sense organs and muscles below the level of the head

Bell-Magendie Law-the entering dorsal roots carry sensory information and the exiting ventral roots carry motor information to the muscles and glands

Dorsal Root Ganglia-clusters of neurons outside the spinal cord

Spinal Cord

• Extends from foramen magnum to second lumbar vertebra

• Segmented– Cervical

– Thoracic

– Lumbar

– Sacral

• Gives rise to 31 pairs of spinal nerves

• Not uniform in diameter throughout length

The spinal cord and spinal nerves

Gross anatomical structures of the spinal cord

A. Two enlargements of the spinal cord occur in

regions where the amount of gray matter is greater than

others; regions of sensory/motor control of the limbs.

1. Cervical enlargement - nerves supply the shoulder and

upper limbs;

2. Lumbar enlargement - nerves supply the pelvis and the

lower limb.

B. Conus medullaris: region at the end of the spinal cord

where the tissue tapers into a cone shape; approximately

in region of L2.

C. Filum terminale: connective tissue, continuous with

the pia mater of the spinal cord.

D. Cauda equina: extension of nerves exiting from the

base of the spinal cord; appears like a horse's tail.

Cross Section of Spinal Cord

Cross Section of Spinal Cord

• White matter:• Myelinated axons

forming nerve tracts• Fissure and sulcus• Three columns:

– Ventral – Dorsal– Lateral

• Gray matter:• Neuron cell cell bodies,

dendrites, axons• ‘Horns’:

– Posterior (dorsal)– Anterior (ventral)– Lateral

• Commissures:– Gray: Central canal – White

(see later for white matter pathways)

Spinal CordIn the spinal cord, the grey matter is found in the centre (the butterfly shape) and the white matter surrounds it. The opposite arrangement is found in the cortex of the brain. Notice the surrounding dura mater .

See ANS lecture

‘Plexus’:intermingling / merging of nerves and subsequent re-organisation--> distribution of peripheral nerves is different from that of spinal nerves

Dermatomal Map• Skin area supplied with sensory innervation by spinal nerves

Equivalent for motor output to muscle groups:Myotome

CNS

PNSsensory motor motor sensory

spinal nerves (31p) cranial nerves (12p)

spinal cord brain

The Organisation of the Nervous System

• Sensory information has to be passed on from the spinal cord to the brain ascending pathways (red)

• Commands from the brain have to be sent out to the PNSdescending pathways (green)

Ascending (afferent) spinal tracts:

• Pathways that carry sensory information to a conscious level

Basic principle of information flow:

• receptor(e.g. pain receptor in skin)

• primary sensory neurone (cell body in dorsal root ganglia)

• second order neurone (in the spinal cord or brainstem)

• third order neurone (in thalamus)

• target area: cortexsomatosensory (somatic sensory) area (postcentral gyrus) of the cortex

Light touch

Conscious perception

Example

Sensory information travels to the brain via 3 main pathways:

To somatosensory cortex (see lecture 3!):1) Spinothalamic system (lateral and anterior tract):somatosensory information to brain:pain and temperature, light touch, pressure, tickle, itch

2) Dorsal column / medial lemniscus:Two-point discrimination, proprioception, pressure, vibration

To cerebellum:3) Spinocerebellar system (posterior and anterior):proprioception, for comparator function (see lecture 2!)

Sensory Nerve Tracts

• Transmit action potentials from periphery to brain

• Each pathway involved with specific modalities

• First half of word indicates origin, second half indicates termination

Pain

• Types– Referred: Sensation in one

region of body that is not source of stimulus

– Phantom: Occurs in people who have appendage amputated or structure removed as tooth

– Chronic: Not a response to immediate direct tissue injury

Descending (efferent) spinal tracts:

• Pathways that carry motor commands from the brain to the muscle

• 2 Systems: direct (pyramidal) and indirect (extrapyramidal)

Basic principle of information flow:

1) Pyramidal System• initiation in (pre-) motor cortex

• upper motor neurone (from motor cortex to brain stem or spinal cord via pyramids) • lower motor neurone (target: muscle)

2) Extrapyramidal System• originate in motor cortex and cerebellum(4 different pathways)

• involve projections via brainstem nuclei

• lower motor neurones(target: muscle)

Unconscious movements(posture, balance, reflexes)

Functions:Muscle tone,voluntary movement

Pyramidal system

SUMMARY: PATHWAYS IN THE SPINAL CORD

Ascending (afferent) pathways (sensation) Descending (efferent) pathways (motor commands)

*

*

Spinal Cord AnatomySpinal Cord Anatomy

Slide 7.53c

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Central canal filled with cerebrospinal fluid

Figure 7.19

Spinal Cord AnatomySpinal Cord Anatomy

Slide 7.54Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Meninges cover the spinal cord

Nerves leave at the level of each vertebrae Dorsal root

Associated with the dorsal root ganglia – collections of cell bodies outside the central nervous system

Ventral root

Peripheral Nervous SystemPeripheral Nervous System


Nerves and ganglia outside the central nervous system

Nerve = bundle of neuron fibers

Neuron fibers are bundled by connective tissue

Structure of a NerveStructure of a Nerve


Endoneurium surrounds each fiber

Groups of fibers are bound into fascicles by perineurium

Fascicles are bound together by epineurium

Figure 7.20

Classification of NervesClassification of Nerves


Mixed nerves – both sensory and motor fibers

Afferent (sensory) nerves – carry impulses toward the CNS

Efferent (motor) nerves – carry impulses away from the CNS

Spinal NervesSpinal Nerves


There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs

Spinal NervesSpinal Nerves

Slide 7.64Copyright © 2003 Pearson Education, Inc. publishing as Benjamin CummingsFigure 7.22a

Autonomic Nervous SystemAutonomic Nervous System


The involuntary branch of the nervous system

Consists of only motor nerves

Divided into two divisions

Sympathetic division

Parasympathetic division

Comparison of Somatic and Comparison of Somatic and Autonomic Nervous SystemsAutonomic Nervous Systems

Slide 7.69Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.24

Anatomy of the Autonomic Nervous Anatomy of the Autonomic Nervous SystemSystem


Figure 7.25

Autonomic FunctioningAutonomic Functioning

Slide 7.74a


Sympathetic – “fight-or-flight”

Response to unusual stimulus

Takes over to increase activities

Remember as the “E” division = exercise, excitement, emergency, and embarrassment

Autonomic FunctioningAutonomic Functioning

Slide 7.74b


Parasympathetic – housekeeping activites

Conserves energy

Maintains daily necessary body functions

Remember as the “D” division - digestion, defecation, and diuresis

Development Aspects of the Development Aspects of the Nervous SystemNervous System

Slide 7.75a


The nervous system is formed during the first month of embryonic development

Any maternal infection can have extremely harmful effects

The hypothalamus is one of the last areas of the brain to develop

Development Aspects of the Development Aspects of the Nervous SystemNervous System

Slide 7.75b


No more neurons are formed after birth, but growth and maturation continues for several years (new evidence!)

The brain reaches maximum weight as a young adult

However, we can always grow dendrites!

Documents

The Nervous System The Spinal Cord-part of the CNS found within the spinal column The spinal cord communicates with the sense organs and muscles below