Spinal Cord and Nerves

1. Spinal Cord and Nerves

2. 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

3. 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

6. 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

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

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

9. 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

10. 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

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

12. 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

13. 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)

14. 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 Nerves (31 Pairs)

15. Spinal Cord Segments

16. 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)

17. 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) Roots V. Rami

18. 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!!

19. 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

20. 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

21. ANS • Includes a chain of 2 motor neurons • Preganglionic neuron • Preganglionic axon • Ganglionic neuron • Postganglionic axon • Autonomic neuron synapses 2 neurons

22. PNS • Somatic NS • Autonomic NS • Sympathetic division • Parasympathetic division • Enteric division

23. 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!

24. 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 CNS – Spinal Cord

26. 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 Spinal Cord Growth

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

28. 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

29. 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 Meninges of Brain and Spinal Cord

30. 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

31. 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 Gray Mater

32. 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

33. 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 White Mater

34. Nervous System Overview