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 Gray matter: Neuron cell cell bodies, dendrites, axons ‘Horns’: Posterior (dorsal) Anterior (ventral) Lateral Commissures: Gray: Central canal White White matter: Myelinated axons forming nerve tracts Fissure and sulcus Three columns: Ventral Dorsal Lateral (see later for white matter pathways)

Spinal Cord In 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 4

intermingling / merging of nerves and subsequent re-organisation ‘Plexus’: intermingling / merging of nerves and subsequent re-organisation --> distribution of peripheral nerves is different from that of spinal nerves 6

Dermatomal Map Skin area supplied with sensory innervation by spinal nerves Equivalent for motor output to muscle groups: Myotome

spinal cord brain CNS PNS The Organisation of the Nervous System spinal nerves (31p) cranial nerves (12p) PNS sensory motor motor sensory 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 PNS descending 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: cortex somatosensory (somatic sensory) area (postcentral gyrus) of the cortex

Example Conscious perception Light touch

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 Anatomy Central canal filled with cerebrospinal fluid Figure 7.19 Slide 7.53c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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

Peripheral Nervous System Nerves and ganglia outside the central nervous system Nerve = bundle of neuron fibers Neuron fibers are bundled by connective tissue Slide 7.55 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Structure 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 Slide 7.56 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Classification 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 Slide 7.57 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Spinal Nerves There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs Slide 7.63 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Spinal Nerves Slide 7.64 Figure 7.22a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Autonomic Nervous System The involuntary branch of the nervous system Consists of only motor nerves Divided into two divisions Sympathetic division Parasympathetic division Slide 7.67 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Comparison of Somatic and Autonomic Nervous Systems Figure 7.24 Slide 7.69 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Anatomy of the Autonomic Nervous System Figure 7.25 Slide 7.73 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Autonomic Functioning Sympathetic – “fight-or-flight” Response to unusual stimulus Takes over to increase activities Remember as the “E” division = exercise, excitement, emergency, and embarrassment Slide 7.74a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Autonomic Functioning Parasympathetic – housekeeping activites Conserves energy Maintains daily necessary body functions Remember as the “D” division - digestion, defecation, and diuresis Slide 7.74b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Development Aspects of the Nervous System 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 Slide 7.75a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Development Aspects of the Nervous System 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! Slide 7.75b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings