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Chapter 13 The Spinal Cord and Spinal Nerves. Functions of the nervous system Sensory (input): –Light –Sound –Touch –Temperature –Taste –Smell –Internal.

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Presentation on theme: "Chapter 13 The Spinal Cord and Spinal Nerves. Functions of the nervous system Sensory (input): –Light –Sound –Touch –Temperature –Taste –Smell –Internal."— Presentation transcript:

1 Chapter 13 The Spinal Cord and Spinal Nerves

2 Functions of the nervous system Sensory (input): –Light –Sound –Touch –Temperature –Taste –Smell –Internal Chemical –Pressure –Stretch

3 Functions of the nervous system (cont’d) Integration: –Integration means making sense of sensory input. Analyzing stimuli based on experience, learning, emotion & instinct and reacting in a useful way (you hope). Motor (output): –The response to the sensory input and subsequent integration. Sending signals to the muscles and other organs of the body instructing them how to respond to the stimuli.

4 Nervous System Organization

5 Overview of Ch 13 & Ch 14

6 The Spinal Cord & Nerves The spinal cord is part of the Central Nervous System. The spinal nerves are part of the Peripheral Nervous System. The lowest level of integration occurs in the spinal cord and peripheral ganglia.

7 Spinal cord: gross anatomy

8 Spinal cord anatomy: the meninges

9 Spinal cord and associated structures

10 Functional arrangement of the spinal cord tissues

11 Cross section of the spinal cord

12 White Matter in the Spinal Cord Fibers run in three directions – ascending, descending, and transversely Divided into three funiculi (columns) – posterior, lateral, and anterior Each funiculus contains several fiber tracks –Fiber tract names reveal their origin and destination –Fiber tracts are composed of axons with similar functions


14 Spinal nerves Thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the head They are named according to their point of issue –8 cervical (C 1 -C 8 ) –12 thoracic (T 1 -T 12 ) –5 Lumbar (L 1 -L 5 ) –5 Sacral (S 1 -S 5 ) –1 Coccygeal (C 0 )

15 Spinal nerve structure

16 Spinal Nerve structure Each axon is also called a “nerve fiber” –These are covered by an endoneurium –The endoneurium is made of areolar c.t. Fibers are bundled into “fascicles” –These are covered by perineurium –This is an extension of the outer layer of collagen fibers Nerves are bundles of fascicles –Each nerve is covered by dense irregular tissue of collagen fibers

17 Components of the Peripheral Nervous System Motor pathways –Leave the spinal cord via the ventral nerve roots. –Have multipolar cell bodies found in the gray matter. –Carry motor impulses to skeletal muscle (somatic pathways) and to glands, smooth muscle, the heart, organs, etc (autonomic pathways). –Are also called efferent pathways.

18 Motor pathways

19 Components of the PNS Sensory Pathways –Enter the cord via the dorsal roots. –Have unipolar cell bodies found in the dorsal root ganglia. –Carry sensory inputs into the CNS via the central processes of their axons. They begin at the general sensory receptors of the skin (somatic sensory) and internal organs (visceral sensory). –Are also known as afferent pathways. –Special sense will be covered in Chapter 17

20 Sensory pathways

21 What’s a damn dermatome?

22 Nerve plexuses

23 Fibers travel to the periphery via several different routes Each muscle receives a nerve supply from more than one spinal nerve Damage to one spinal segment cannot completely paralyze a muscle

24 Cervical plexus

25 Table 13-1 Summary: Cervical Plexus

26 Brachial plexus

27 Fig a The brachial plexus

28 Some common injuries to the brachial plexus Study question: Which nerves are affected here?

29 Table 13–2 (1 of 2) Summary: Brachial Plexus

30 Table 13–2 (2 of 2) Summary: Brachial Plexus

31 Lumbar and sacral plexuses

32 Table 13-3 (1 of 2) Summary: Lumbar and Sacral Plexuses

33 Table 13-3 (2 of 2) Summary: Lumbar and Sacral Plexuses

34 Lumbar & sacral plexus nerves

35 Neural circuits

36 Neural Circuits Divergent – spread information from one source to several destinations. –Examples: visual input being processed at a conscious level (the horizon is tilting) and a subconscious level (I adjust my body so that I don’t fall over). Convergent – multiple sources of input into one neuron. –Examples: conscious – I contract my rectus femoris to step over a pile of dog poop. Unconscious – my rectus femoris automatically contracts as the bus moves

37 Neural Circuits Serial – a series of neurons in a sequence. –Example: Pain pathways Parallel – Divergence followed by serial. –Example – reflexes that result in a complex series of responses simultaneously Reverberation – positive feedback loops –Examples – many of the complex processes of the brain.

38 Reflexes Rapid, automatic responses to stimuli. Can be visceral (e.g. swallowing) or somatic (“knee-jerk”). Have little variability


40 Components of a reflex arc 1.Stimulus activates a receptor. 2.Impulse travels along a sensory pathway. 3.Integration occurs in an integration center (most often in the CNS) 4.Impulse then travels by a motor pathway. 5.An effector responds.

41 4 Classifications of Reflexes 1.By early development 2.By type of motor response 3.By complexity of neural circuit 4.By site of information processing

42 Development How reflex was developed: –innate reflexes: basic neural reflexes formed before birth –acquired reflexes: rapid, automatic learned motor patterns

43 Response Nature of resulting motor response: –somatic reflexes: involuntary control of nervous system –superficial reflexes of skin, mucous membranes –stretch reflexes (deep tendon reflexes) e.g., patellar reflex –visceral reflexes (autonomic reflexes): control systems other than muscular system e.g., glands smooth muscle and cardiac muscle

44 Complexity Complexity of neural circuit: –monosynaptic reflex: sensory neuron synapses directly onto motor neuron –polysynaptic reflex: at least 1 interneuron between sensory neuron and motor neuron

45 Processing Site of information processing: –spinal reflexes: occurs in spinal cord –cranial reflexes: occurs in brain

46 Monosynaptic: Stretch reflex

47 Monosynaptic Reflexes Have least delay between sensory input and motor output: –e.g., stretch reflex (such as patellar reflex) Completed in 20–40 msec

48 Muscle Spindles The receptors in stretch reflexes Bundles of small, specialized intrafusal muscle fibers: –innervated by sensory and motor neurons Surrounded by extrafusal muscle fibers: –which maintain tone and contract muscle

49 Muscle spindles

50 Postural Reflexes Postural reflexes: –stretch reflexes –maintain normal upright posture Stretched muscle responds by contracting: –automatically maintain balance

51 Polysynaptic Reflexes More complicated than monosynaptic reflexes Interneurons control more than 1 muscle group Produce either EPSPs or IPSPs

52 Polysynaptic: Flexor

53 The Tendon Reflex Prevents skeletal muscles from : –developing too much tension –tearing or breaking tendons Sensory receptors unlike muscle spindles or proprioceptors

54 Withdrawal Reflexes Move body part away from stimulus (pain or pressure): –e.g., flexor reflex: pulls hand away from hot stove Strength and extent of response: –depends on intensity and location of stimulus

55 Reflex Arcs Ipsilateral reflex arcs: –occur on same side of body as stimulus –stretch, tendon, and withdrawal reflexes Crossed extensor reflexes: –involves a contralateral reflex arc –occurs on side opposite stimulus

56 Figure 13–18 The Crossed Extensor Reflex

57 5 General Characteristics of Polysynaptic Reflexes 1.Involve pools of neurons 2.Are intersegmental in distribution 3.Involve reciprocal inhibition 4.Have reverberating circuits: –which prolong reflexive motor response 5.Several reflexes cooperate: –to produce coordinated, controlled response

58 Figure 13–19 The Babinski Reflexes Normal in infants May indicate CNS damage in adults

59 Spinal Cord Trauma: Paralysis Paralysis – loss of motor function Flaccid paralysis – severe damage to the ventral root or anterior horn cells –Lower motor neurons are damaged and impulses do not reach muscles –There is no voluntary or involuntary control of muscles

60 Spinal Cord Trauma: Paralysis Spastic paralysis – only upper motor neurons of the primary motor cortex are damaged –Spinal neurons remain intact and muscles are stimulated irregularly –There is no voluntary control of muscles

61 Spinal Cord Trauma: Transection Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut Paraplegia – transection between T 1 and L 1 Quadriplegia – transection in the cervical region

62 Spinal cord transection

63 Poliomyelitis Destruction of the anterior horn motor neurons by the poliovirus Early symptoms – fever, headache, muscle pain and weakness, and loss of somatic reflexes Vaccines are available and can prevent infection

64 Some effects of Polio

65 Amyotrophic Lateral Sclerosis (ALS) Lou Gehrig’s disease – neuromuscular condition involving destruction of anterior horn motor neurons and fibers of the pyramidal tract Symptoms – loss of the ability to speak, swallow, and breathe Death often occurs within five years Linked to malfunctioning genes for glutamate transporter and/or superoxide dismutase

66 Some Famous Victims of ALS Lou Gehrig Steven Hawking, renowned physicist

67 Axonal degeneration of motor neurons evident in lateral corticospinal (pyramidal) pathways, especially in the loss of myelinated fibers of the corticospinal tracts

68 SUMMARY (1 of 7) General organization of nervous system: –CNS, PNS Gross anatomy of spinal cord: –enlargements, dorsal and ventral roots, filum terminale, conus medullaris

69 SUMMARY (2 of 7) Afferent (sensory) and efferent (motor) fibers Structures and functions of spinal meninges Gray matter and horns of spinal cord

70 SUMMARY (3 of 7) White matter and columns (tracts) of spinal cord 3 layers in spinal nerves Distribution (rami) of spinal nerves: –white, gray, dorsal, ventral

71 SUMMARY (4 of 7) 4 major nerve plexuses: –cervical, brachial, lumbar, sacral Neuronal pools and neural circuit patterns: –divergence, convergence, serial, parallel, reverberation

72 SUMMARY (5 of 7) Reflexes and reflex arcs Classifications of reflexes: –innate vs. acquired –somatic vs. visceral –cranial vs. spinal –monosynaptic, polysynaptic, or intersegmental

73 SUMMARY (6 of 7) Characteristics of monosynaptic reflexes: –stretch reflex, postural reflex, muscle spindles Characteristics of polysynaptic reflexes: –tendon, withdrawal, flexor, and crossed extensor reflexes

74 End Chapter 13

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