Lesson 5 Flashcards
2 main functions of the spinal cord
- Propagates nerve impulses
- Integrates information
2 main sensory tracts
Spinothalamic tract: conveys nerve impulses for sensing pain, temperature, itch, tickle, and touch, pressure, vibration
Posterior column: made up of 2 tracts gracile fasciculus & cuneate fasciculus
- conveys nerve impulses for touch, light
pressure, vibration and conscious
proprioception
Conscious proprioception:
the awareness of the positions and movements of muscles, tendons and joints
2 main motor tracts
Direct pathways:
- nerve impulses originate in cerebral cortex
- cause voluntary movements of skeletal muscle
Indirect pathways:
nerve impulses originate in brain stem
- causes automatic movements
- helps coordinate body mvts with visual stimuli
- maintains skeletal muscle tone
- sustained contraction of postural muscles
- major role in equilibrium by regulating muscle
tone in response to movements of head
Stimulus
a change in the internal or external environment
Reflex
a fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus
- can be inborn or learned
Types of reflexes
- Spinal reflex -when integration happens in grey matter of SC
- Cranial reflex - -when integration happens in brain stem
- Somatic reflex - -involves contraction of skeletal muscle
- Autonomic reflexes - -involves contraction of skeletal muscle
-not usually consciously perceived
-involve responses of smooth mm, cardiac mm and glands
Reflex Arc
-the reflex arc or reflex circuit is the pathway for nerve
impulses that produce a reflex
-it’s made up of 5 things:
- Sensory receptor
responds to stimulus by producing a generator or receptor potential
- Sensory neuron
Axon conducts impulses from receptor to integrating center
- Integrating center
monosynaptic reflex arc – most simple
-a reflex pathway with only 1 synapse in the CNS
(so 2 neurons and 1 synapse)
Polysynaptic reflex arc
- when the integrating center consists of at least
one interneuron
- involves more than 1 synapse in the CNS
(so 3 neurons and 2 synapses)
- Motor Neuron
Axon conducts impulses from integrating center to effector
- Effector
mm or gland responds to motor nerve impulses
The stretch reflex
-contraction of a skeletal muscle in response to stretching of that muscle
-monosynaptic reflex arc
Stretch reflex can be elicited by
-can be elicited by tapping on tendons attached to muscles at elbow, wrist, knee and ankle joints
Stretch reflex muscle spindles
- stimulates muscle spindles
- muscle spindles are sensory receptors in the mm
- they monitor the change in length of the mm
- the stretch reflex is an ipsilateral reflex
- sensory nerve impulses enter the same side
that the motor nerve impulses come out
The stretch reflex
-tone of a muscle is also set through muscle spindles
Muscle tone = the small degree of contraction present
when a muscle is at rest
The stretch reflex
Reciprocal innervation
when parts of a neural circuit simultaneously cause contraction of 1 muscle and relaxation of its antagonists
-the stretch reflex helps avoid injury
by preventing overstretching of the muscle
The tendon reflex
-relaxation of a muscle when there is too much tension
-prevents tearing of a tendon
-ipsilateral
-polysynaptic
-stimulates Golgi tendon organs (GTO)
GTO: sensory receptor monitors
changes in mm tension
The tendon reflex
-this reflex protects the tendon and muscle from damage due to
excessive tension
-reciprocal innervation
The flexor (withdrawal) reflex
when you step on a tack, you will flex or withdraw your leg away from the painful stimulus
-it is a polysynaptic reflex arc
-it is ipsilateral
-this is a protective reflex because it moves the limb away from a possibly damaging stimulus
intersegmental reflex arc
-nerve impulses from 1 sensory neuron ascend and descend in the spinal cord, activating interneurons in several segments of the spinal cord
-this way a single sensory neuron can activate several motor neurons
The crossed extensor reflex
-happens with the flexor reflex
-when you step on a tack and withdraw or flex your leg, the other leg needs to extend so you don’t fall over
-this is a contralateral reflex arc
-sensory impulses enter one side of the spinal cord and motor impulses exit on the opposite side
-intersegmental reflex arc
-reciprocal innervation
