Practical Exam 2 - Nervous System and Neurology Flashcards
(119 cards)
Stimulus-response reaction
All living things must detect changes in the environment and react appropriately; Involves receptors that detect change, sensory neurons, which send the information to the central nervous system where it is processed, and motor neurons that send the information to effectors that produce a response appropriate to the situation; If motor response is initiated, it usually involves a series of action potentials that produce a muscle contraction and a movement of one or more parts of the body; Example: Reflexes
Learned reflexes
Result from repetition; Example: Reflexes needed to drive a car where, with practice, the activity is mostly automatic and subconscious
Inborn reflex
A rapid, predictable, involuntary, and unlearned, motor response to a stimulus, and is part of all our neural pathways; Below consciousness and do things like keep us breathing, maintain posture, and avoid pain; An inborn reflex to a painful stimulus can be so rapid that a response is generated before you can even perceive the pain; Many inborn reflexes are regulated by the spinal cord; Example: Myotatic reflex
Myotatic reflex
Produced by a tap on the tendon under the kneecap; Knee-jerk reflex; Simple spinal reflex;
Employs only four neurons; Striking the patellar ligament just below the patella stretches the quadriceps muscle; This stimulates sensory muscle spindle receptors in the muscle that trigger an impulse in a sensory axon whose cell body lies in the dorsal root ganglion in the lumbar region of the spinal cord; The sensory axon synapses directly with a motor neuron that conducts the impulse to the quadriceps, triggering contraction in extrafusal fibers of the stretched muscle; Sensory axon also has reciprocal inhibition;
Patellar knee-jerk reflex is tested to determine if motor and sensory connections between the spinal cord and the thigh muscles are functioning
Brain not required
5 parts of reflex arcs
1) The receptor that senses the stimulus and initiates the signal
2) A sensory neuron that carries afferent nerve impulses to the central nervous system
3) An integration center where the signal is processed; Either a single synapse, a few synapses and interneurons, or the central nervous system
4) The motor neuron that carries efferent signals to the effector from the integration center
5) The effector such as a muscle or a gland which generates a response to a signal
Monosynaptic reflex
Signal is processed at a single synapse between a motor and sensory neuron
Polysynaptic reflex
Signal is processed by a few synapses and interneurons
Somatic reflex
Activates skeletal muscle
Autonomic reflex
Controls visceral effectors such as smooth muscle, cardiac muscle, or a gland
Spinal reflexes
Do not involve higher brain centers to function; Brain often receives communication from these reflexes and can facilitate or, at least partially, inhibit the reflex; Produced via single synapses between sensory axons and motor neurons; Essential central circuitry is confined to the spinal cord
What indicate damage to the nervous system
Distorted, exaggerated, or absent reflexes indicate damage to the nervous system
Proprioceptors
Receptors that supply information to the central nervous system about the body’s position in space and how much a muscle has moved, or not moved, in its insertion; Examples: Muscle spindles and Golgi tendon organs
Muscle spindles and Golgi tendon organs
Proprioceptors
Muscle spindles in a skeletal muscle convey information about muscle length or the amount of stretch
Golgi tendon organs convey information about tendon tension so that proper regulation of these reflexes takes place
Reciprocal inhibition
In spinal reflex, sensory axon synapses in the spinal cord with an inhibitory interneuron that, in turn, synapses with a motor neuron that conducts impulses to the antagonistic muscle to inhibit contraction; This allows for contraction of the stretched muscle without impedance from the basal muscle tone of the opposing muscle
Stretch and tendon reflexes
Stretch and tendon reflexes help coordinate smooth movements of skeletal muscle groups
Stretch reflexes
Stimulates muscle contraction when muscle length is increased or the muscle is stretched; All stretch reflexes are ipsilateral and monosynaptic in the contracting portion of the pathway; The inhibitory portion of the pathway in the reflex arc is polysynaptic making the total stretch reflex also technically polysynaptic
Ipsilateral
Involves motor activity on the same side of the body
Tendon reflex
Polysynaptic; Opposite of stretch reflex; Causes muscles to relax in circumstances of high tendon tension
Magnitude of response indicates
Magnitude of response indicates the level of inhibition being processed at the spinal cord; Many biological processes are largely regulated by controlling inhibition and the brain prevents extraneous movements of the body by sending out inhibitory signals to prevent awkward and uncoordinated movements
Exaggerated reflex
Could indicate damage to the brain or spinal cord
Absent reflex
Could indicate damage of peripheral nerves
Complex reflexes
Usually involve additional cells, interneurons, and more than one population of motor neurons; results in a longer delay between stimulus reception and the more complex response; Example: Pupillary reflex
Pupillary reflex
Direct light reflex; Example of a complex reflex; Involves four neurons that connect the retina to the mid-brain and then convey information back to the pupillary sphincter muscles; When light is focused upon the eye, the pupillary sphincter muscle in the iris constricts reducing the diameter of the pupil; At the same time, the pupillary sphincter of the other eye constricts too; Miosis; Consensual light reflex
Consensual light reflex
When light is focused upon one eye, the diameter of the pupil constricts; At the same time, the diameter of the other eye constricts as well, even if there is no light shining in the eye
