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anatomy
chapter 16 part 2
45
Anatomy
Undergraduate 1
04/12/2012

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Term
Tract
Definition

bundles of axons in CNS

Nerve impulse “highways”  between spinal cord and brain

Term
Sensory (ascending) tracts
Definition
consist of axons that conduct nerve impulses toward the brain
Term
Sensory (ascending) tracts
Definition

Keep CNS informed of changes in external and external environment; this information is integrated or processed by interneurons in spinal cord and brain
 
Term
Motor (descending) tracts
Definition
consist of axons that carry nerve impulses away from the brain
Term
Motor (descending) tracts
Definition

Responses to integrative decisions are brought about by motor activities (muscular contractions and glandular secretions)

 
Term
White matter of spinal cord 
Definition
contains both sensory and motor tracts
Term
Spinothalamic tract
Definition
sensory (ascending) tract that conveys nerve impulses for sensing pain, warmth, coolness, itching and tickling to CNS
Term
Corticospinal tract
Definition
motor (descending) tract that conveys nerve impulses that originate in brain and are destined to cause voluntary movements of skeletal muscles
Term
White matter of spinal cord 
Definition
cord contains sensory and motor tracts, the “highways” for conduction of sensory nerve impulses toward the brain and motor nerve impulses from the brain toward effector tissues
Term
Gray matter of spinal cord 
Definition
cord is a site for integration (summing) by interneurons of incoming excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs)
Term
Spinal nerves and the nerves that branch from them
Definition
connect the CNS to the sensory receptors, muscles, and glands in all parts of the body
Term
reflex 
Definition
is a fast and automatic involuntary response to a specific stimulus
Term
Inborn Reflex
Definition
pulling hand away from hot surface
Term
Learned Reflex
Definition
slam on car brakes during emergency
Term
Spinal reflex
Definition

involves spinal cord gray matter

Patellar (knee-jerk) reflex

 
Term
Cranial reflex
Definition

involves brain stem

Tracking movements of eyes while reading

 
Term
Somatic reflex
Definition
involves contraction of skeletal muscles
Term
Autonomic (visceral) reflex
Definition
involves unconscious responses of smooth and cardiac muscle, and glands
Term
Reflex arc
Definition
pathway followed by nerve impulses that produce a reflex. 
Term
5 Components of a reflex arc
Definition

1.  Sensory receptor

2.  Sensory neuron

3.  Integrating Center

4.  Motor Neuron

5.  Effector

Term
1.  Sensory receptor
Definition

distal end of a sensory neuron (dendrite) or an associated sensory structure

Detects/responds to specific stimulus (change in internal or external environment)

Produces a graded potential – if it reaches threshold it will trigger nerve impulse in sensory neuron

 
Term
Sensory neuron
Definition
sends nerve impulse along its axon to the integrating center
Term
.  Integrating Center
Definition

located in gray matter of CNS

Brainstem: for cranial reflexes

Spinal Cord: for spinal reflexes

 
Term
Monosynaptic reflex
Definition
only one synapse between sensory and motor neuron (no interneurons)
Term
Polysynaptic reflex
Definition
interneurons occur between sensory and motor neurons, more than one synapse involved
Term
Motor Neuron
Definition
Sends nerve impulse away from integrating center to effectors
Term
Effector
Definition

part of the body that produces response

Skeletal muscles in somatic reflex 

Cardiac or smooth muscles or glands in autonomic reflex

 
Term

The Stretch Reflex

 
Definition

Causes contraction of a skeletal muscle in response to stretching of the muscle.

Helps maintain posture

 
Term
Ipsilateral:
Definition
sensory nerve impulses enter the spinal cord on the same side from which motor impulses leave it (entire reflex arc on same side of body)
Term
Patellar or knee-jerk reflex
Definition
: Stretching of quadriceps femoris muscle →activation of sensory receptors →sensory neuron →spinal cord→motor neuron → contraction of quadriceps femoris muscle.
Term
Protective reflex
Definition
contraction of flexor muscles moves a limb away from source of possible damaging stimulus
Term
Intersegmental:
Definition

nerve impulses from one sensory neuron ascend and descend in spinal cord and activate interneurons in several segments of spinal cord

Allows stimulation of more than one effector e.g. to move an entire upper or lower limb involves contraction of several limb muscles!

Stepping on a tack (stimulus) → activation of sensory receptor → nerve impulse → activation of several interneurons → activation of motor neurons →muscle contraction of flexor muscles→withdrawal of the leg.

 
Term
absent or abnormal
Definition
Damage or disease anywhere along a reflex arc can cause a reflex to be
Term
Patellar reflex
Definition

absence of this somatic reflex could mean damage of motor or sensory neurons, or spinal cord injury in 2nd, 3rd or 4th lumbar segments of spinal cord

Often absent in people with chronic diabetes mellitus

 
Term
Positive Babinski sign
Definition

somatic reflex where great toe dorsiflexes to gentle stroking of lateral outer margin of sole 

Normal for children under 18 mos. of age

Abnormal after 18 mos. of age: damage to corticospinal tract

 
Term
Negative Babinski sign
Definition
curling under of all toes
Term
Pupillary light reflex
Definition

autonomic reflex where pupils of both eyes decrease in diameter when either eye is exposed to light

Absence indicates brain damage or injury

 
Term
Spinal Cord Injury
Definition

Spinal cord injury outcomes range from little to no long-term effects to paralysis or even death.

Most spinal cord injuries are due to trauma as a result of automobile accidents, falls, contact sports, diving, or acts of violence

Effects of injury depend on extent of direct trauma to spinal cord or compression of the cord by fractured or displaced vertebrae or blood clots.

Common sites of injury are in cervical, lower thoracic and upper lumbar regions

Patients may have improved outcome if an anti-inflammatory corticosteroid is given within 8 hrs of injury

Decreases edema (collection of fluid in tissue) due to immune response to injury

Term
Complete transection
Definition

spinal cord is severed from one side to another

Cuts all sensory and motor tracts

Loss of all sensations and voluntary movement below level of transection

 
Term
C1-C3
Definition
quadriplegic; ventilator needed for breathing
Term
C4-C5
Definition
quadriplegic, can breathe
Term
T1-T9
Definition
paraplegic; can use arms
Term
T10-L1
Definition
most thigh muscles can be used; walk with long leg braces
Term
L1-L2
Definition
most leg muscles can be used; walk with some assistance
Term
Stretch Reflex 
Definition

Stretch reflex pathway is monosynaptic, however a polysynaptic reflex arc to the antagonistic muscles operates at the same time

Three neurons and two synapses

Inhibitory interneuron inhibits a motor neuron that would normally excite antagonistic muscles

Prevents conflict between opposing muscles and is vital in coordinating body movements

Axon collaterals of sensory neuron also relay nerve impulses to the brain over specific ascending tracts

Brain receives input of stretch or contraction of skeletal muscles, enables it to coordinate movements

Allows conscious awareness that the reflex has occurred.

 
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