Spinal Cord and Nerves The Nervous System n

Spinal Cord and Nerves

The Nervous System n Coordinates the activity of muscles, organs, senses, and actions n Made up of nervous tissue n Has 3 main functions: 1. Receives sensory Input n 2. Integration n 3. Dictates motor output n

Divisions of the Nervous System n Central Nervous System (CNS) n Brain and spinal cord n Interprets incoming sensory signals n Dictates motor responses n Peripheral Nervous System (PNS) n Ganglia n Nerves n n Cranial nerves and spinal nerves Communication between regions of body and CNS

Somatic PNS ANS Sympathetic Parasymp. Enteric CNS

PNS n Nervous system structures outside the brain and spinal cord n Either somatic or visceral n Visceral motor portion is the ANS n Structural components: n Sensory receptors n Motor endings n Nerves and ganglia

PNS - Nervous Tissue n Made up of 2 cells: n Neurons n Conduct electrical impulses n Supporting cells n Surround the neurons n Ex. Glial cells

The Neuron n Nerve cells n Transmit signals in form of nerve impulses n Have extreme longevity n Do not divide n High metabolic rate

Neuronal Anatomy n Cell body (soma) Most are in CNS n Neuron processes n Dendrites n n n Toward cell body Axons n Transmit away from cell body n Synapses n Site where neurons communicate

Neuronal Anatomy n Myelin sheath n Fatty sheath that surrounds most nerve fibers n Reflex arc n Responses to a stimulus n Interneuron n Nerve cell that lies between a sensory neuron and motor neuron in a reflex arc n Confined entirely within the CNS

PNS - Sensory and Motor Signals n Divided by the body regions they serve: n Sensory division n Somatic sensory n Visceral sensory n Motor division n Somatic motor n Visceral motor

Types of Nerve Signals/Fibers n Sensory (afferent) n Picked up by sensory receptors thru body n Carried by nerve fibers of PNS into CNS n Motor (efferent) n Carried away from the CNS by nerve fibers into PNS n Innervate muscles and glands n Causes these organs to contract or secrete n Remember: SAME

Sensory and Motor Signals/Fibers n Somatic sensory Body senses n touch, pressure, temperature, vibration of body, muscles stretching, balance n Visceral sensory n Organ senses n Stretch, pain, temperature in organs n (eg) nausea, hunger, cramps n Somatic motor n Body movement n Voluntary contraction of skeletal muscles n Visceral motor n Organ movement n Contraction of smooth muscle, glands n = Autonomic Nervous System (involuntary) n

Spinal Nerves (31 Pairs) n Part of the PNS (Somatic) n Lie in intervertebral foramina Send lateral branches to body n Named according to their point of issue from the vertebral column n 8 pairs of cervical spinal nerves; C 1 -C 8 n 12 pairs of thoracic spinal nerves; T 1 -T 12 n 5 pairs of lumbar spinal nerves; L 1 -L 5 n 5 pairs of sacral spinal nerves; S 1 -S 5 n 1 pair of coccygeal spinal nerves; C 01 n

Spinal Cord Segments

Spinal Nerves n Each spinal nerve connected to spinal cord via dorsal (sensory) and ventral (motor) root n Spinal nerves branch into dorsal ramus and ventral ramus n Ventral ramus n n n Connects to rami communicates, which then lead to sympathetic chain ganglia Supply anterior and lateral regions of the neck, trunk, and limbs Dorsal ramus n Supply the dorsum of the neck and trunk (back)

Roots V. Rami n Lateral branches of spinal nerves n Each contains both sensory fibers and motor fibers n Roots n Lie medial to the spinal nerves n Strictly sensory (dorsal) or motor (ventral)

The Big Picture n Just lateral to intervertebral foramen, each spinal nerve then splits in 2 n n Dorsal Rami Ventral Rami n Contain BOTH Sensory and Motor fibers!!

Autonomic Nervous System n Visceral Motor Function n Not easily controlled by will n Get nervous and sweat n Innervate smooth muscle, cardiac muscle, glands n Regulate visceral function n Heart rate, blood pressure, digestion, urination n Has 2 divisions: n Parasympathetic n Sympathetic

ANS n Parasympathetic n Enables body to unwind and calm down n Most active when body at rest n Routine maintenance functions n Craniosacral division n Fibers emerge from brain and sacral spinal cord n Sympathetic n “fight or flight” n Mobilizes the body during extreme situations n Becomes active when extra metabolic effort needed n Thoracolumbar division n Fibers arise from thoracic and lumbar parts of spinal cord

ANS n Includes a chain of 2 motor neurons n Preganglionic neuron n Preganglionic axon n Ganglionic neuron n Postganglionic axon n Autonomic neuron synapses 2 neurons

PNS n Somatic NS n Autonomic NS n Sympathetic division n Parasympathetic division n Enteric division

Somatic Nervous System n Innervates skeletal muscle n Neurons runs from CNS directly to muscle n Consists of single neuron plus skeletal muscle cells n Voluntary control n Running, moving limbs, typing on a computer!

CNS – Spinal Cord n Runs through vertebral canal of the vertebral n n 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: n n n 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 n Until 3 rd month of n n development, does not run to coccyx As vertebral column grows caudally, spinal cord becomes more rostral At birth, ends at L 3 During childhood, terminates at L 1 and L 2 Adults runs from medulla oblongata to L 1

Regions of the Spinal Cord n Cervical n Thoracic n Lumbar n Sacral n Coccygeal n Cervical + Lumbar enlargements n Cauda equina n Conus medullaris n Filum terminale

Meninges of Brain and Spinal Cord n Dura mater (superficial) Spinal dural sheath n Does not attach to bone n Epidural space n Fat and veins n Between dura mater and vertebra n Subdural space n n Between dura mater and arachnoid

Meninges of Brain and Spinal Cord n Arachnoid mater (middle) Impermeable layer = barrier n Raised off pia mater by rootlets n Subarachnoid space n Between arachnoid and pia mater n Contains CSF n Pia mater (deep) n Highly vascular n Adheres to brain/spinal cord tissue n

Gray Mater n Consists of neuron cell bodies, unmyelinated axons, dendrites, and neuroglia n Shaped like an “H” n n Gray commissure (crossbar) Central canal n Posterior horns n Anterior horns

Gray Mater n Posterior horns n n Consist of interneurons that transmit in from outside spinal cord into it Dorsal root contain sensory fibers n n Somatic Sensory (SS) Visceral Sensory (VS) Dorsal root ganglia - swelling in dorsal root that these interneurons pass through n Anterior horns n Cell bodies of motor neurons send info out of spinal cord to muscles and glands n Ventral Root contains Motor Fibers n n n Visceral Motor Somatic Motor

White Mater n Surrounds gray matter n Composed of myelinated and unmyelinated axons n Divided into white columns (funiculi) n n n Posterior funiculus Anterior funiculus Lateral funiculus n Allow for communication between n n Parts of the spinal cord Spinal cord and brain

White Mater n 3 types of nerve fibers: n Ascending n n n Descending n n Carry sensory info from sensory neurons of body to brain touch, pressure, pain, temperature 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 n Cross from one side of cord to the other

Nervous System Overview