Presentation is loading. Please wait.

Presentation is loading. Please wait.

Unit IV: Coordination Reflex Arc

Similar presentations


Presentation on theme: "Unit IV: Coordination Reflex Arc"— Presentation transcript:

1 Unit IV: Coordination Reflex Arc
Chapter 11 – pp Chapter 12 – pp

2 Internal Coordination
Endocrine and nervous system maintain internal coordination endocrine = nervous = Reflex Arc: sense organs receive information brain and spinal cord determine responses brain and spinal cord issue commands to glands and muscles

3 Subdivisions of Nervous System
Central nervous system (CNS) Peripheral nervous system (PNS) Brain Two major anatomical subdivisions Central nervous system (CNS) Peripheral nervous system (PNS) consists of nerves and ganglia Spinal cord Nerves Ganglia

4 Neural Tissue A nerve is a bundle of nerve fibers (axons) wrapped in fibrous connective tissue. emerge from the CNS to carry signals between organs Neurons and neuroglial cells

5 Functions of Neurons Excitability (irritability) stimuli Conductivity
produce traveling electrical signals Secretion at end of nerve fiber, a neurotransmitter is secreted

6 Structure of a Neuron Soma (cell body) Dendrites Axon (nerve fiber)
trigger zone Myelin Sheath some nerve fibers insulating layer (mostly lipid) formed by neuroglia

7 A Representative Neuron

8 Functional Classes of Neurons

9 Structural Classes of Neurons
Dendrites Axon Synaptic terminals Structural Classes of Neurons Cell body Dendrites Dendritic process Axon Synaptic terminals Multipolar neuron Bipolar neuron Unipolar neuron Peripheral fiber carries impulses from source of sensation Central fiber carriers impulses to spinal cord Anaxonic neuron Dendrites Initial segment Axon Synaptic terminals

10 Neuroglial Cells Also known as Glial cells Outnumber neurons
General functions: Protect Support, maintain physical structure of neural tissue Repair Maintain nutrient supply to neurons

11 Types of Neuroglial Cells
Occur in the Central Nervous System Oligodendrocytes form myelin sheaths in CNS Ependymal cells line cavities of brain and spinal cord produce and circulate CSF Microglia macrophages (WBC) Phagocytosis in areas of infection, trauma or stroke

12 Types of Neuroglial Cells
Astrocytes most abundant glial cells cover brain surfaces formation of blood-brain barrier regulate composition of cerebrospinal fluid remove neurotransmitters and potassium ions from ICF repairing damaged tissue with scar tissue Occur in the Peripheral Nervous System Schwann cells form myelin sheath in PNS Satellite cells surround somas of neurons in ganglia

13 Neuroglial Cells of CNS
Section of spinal cord Ependymal cell Microglial cell Neurons Gray matter White matter Myelinated axons Astrocytes Oligodendrocyte Capillary Axon Myelin (cut) Nodes Unmyelinated axon

14 Myelination

15 Demyelination Hallmark of some neurodegenerative autoimmune diseases:
Multiple Sclerosis Demyelination in CNS Own immune system attacks and damages myelin Scars form in white matter of CNS Cause unknown, no cure Cerebral Palsy Damage to developing oligodendrocytes usually during infancy Mutations, lack of oxygen, interruption of blood flow Treatment of symptoms, no cure Leukodystrophies Results from defect in the gene that controls the production of only one component molecule of myelin Affects growth and maintenance of white matter Inherited, no cure

16 Nerve Signal Depends on two factors: Presence/absence of myelin
Diameter of fiber - large/thicker fibers have more surface area for signals Functions fast signals employed when speedy responses are needed slow signals used when quick responses are not important

17 Regeneration of Nerve Fiber in PNS
Axon Myelin Step 1: the axon and myelin degenerate and fragment. Step 2: The Schwann cells proliferate and macrophages remove the debris distal to the injury site. Macrophage Regeneration Tube Step 3: The axon grows along the path created by the Schwann cells. Step 4: As the axon elongates, the Schwann cells wrap around it. Site of injury

18 Reflexes Properties: Require stimulation Quick Involuntary Stereotyped
Reflex Arc: Somatic receptors → afferent nerves → integrating center → efferent nerves → skeletal muscles

19 The Stretch Reflex When a muscle is stretched, it contracts and maintains increased muscle tone (stretch reflex) helps maintain equilibrium and posture balances tension in extensors and flexors mediated by the brain Reciprocal inhibition prevents muscles from working against each other Very sudden muscle stretch causes tendon reflex knee-jerk (patellar) reflex is monosynaptic reflex

20 The Tendon Reflex 6 Primary afferent neuron stimulates
inhibitory interneuron To brain 4 Primary afferent neuron stimulates alpha motor neuron to extensor muscle 7 Interneuron inhibits alpha motor neuron to flexor muscle 5 Alpha motor neuron stimulates extensor muscle to contract 3 Primary afferent neuron excited 2 Muscle spindle stimulated 1 Extensor muscle stretched 8 Flexor muscle (antagonist) relaxes

21 Flexor (Withdrawal) Reflexes
Occurs during withdrawal of a limb from pain Contract flexor muscles Polysynaptic reflex arc Not just one sudden response as in stretch reflex Ipsilateral reflex arc

22 Crossed Extensor Reflexes
Maintains balance by extending other limb Contract extensor muscles Contralateral reflex arcs explained by pain at one foot causes muscle contraction in other leg

23 Golgi Tendon Reflex Golgi tendon organs in a tendon near its junction with a muscle Excessive tension on tendon inhibits motor neuron muscle contraction decreased Also functions when some parts of muscle contracts more than others


Download ppt "Unit IV: Coordination Reflex Arc"

Similar presentations


Ads by Google