Reflexes COPY Flashcards
What is a reflex ?
A specific, involuntary, unpremeditated, “built-in” response to a particular stimulus.
Give an example of an acquired reflex ?
Many operations during car driving
What is the relation between homeostasis and reflexes ?
Reflexes are a component of homeostatic control systems
Are we conscious of our reflexes ?
We are conscious of some of them
Describe the steps of the homeostatic mechanism initiated as a result of decreased room temperature and identify the reflex as part of this mechanism.
Decreased room temperature –> Increased heat loss from body –> Decreased body temperature –>
Reflexes: 1) (curling up –> Decreased heat loss from body) + 2) (constriction of skin blood vessels –> Decreased heat loss from body) + 3) (shivering –> Increased heat production) –> Return of body temperature towards original value.
What is the reflex arc ? What are the components of a reflex arc ?
The pathway mediating a reflex
Stimulus: Detectable change in internal/ external environment
Receptor: Detects the stimulus
Integrating center: Receives the signal and compares it to set point
Effector: Produces a response
Response: Sometimes gives negative feedback (back to stimulus)
Is the spinal/motor reflex conscious ?
No, it does not involve conscious thought
What is the sensory, and what is the efferent component of the spinal/motor reflex ?
Sensory component = sensory receptor
Effector component = motor outflow from the spinal cord to the appropriate muscles
What is a monosynaptic reflex ? Give an example of monosynaptic reflex.
A simple reflex that involves transmission of information from a sensory neuron to the appropriate motor neuron across a single synapse in the spinal cord.
E.g. Knee-jerk reflex
How are Axons routed to the CNS ?
Insides nerves
How many axons are there per nerve ?
Rypically there are many axons from many neurons inside one nerve
Is is possible for single nerves to carry both sensory and motor axons ? How is this useful ?
Yes
Because information can travel in two directions in a nerve.
What do the principal differences between different axons lie in ?
- Diameter
2. Myelination
Why is it that, if you record the activity in a nerve following a stimulation, you get multiple peaks ?
Because there are different fibre types within a nerve, all of which have different properties.
What are the types of nerve fiber types, when classified by conduction velocity ?
Aα Aβ Aγ Aδ B C
What is the function of the different nerve fiber types (different types based on conduction velocity) ?
Aα: Proprioception, somatic motor Aβ: Touch, pressure Aγ: Motor to muscle spindles Aδ: Pain Temperature B: Preganglionic automic C: Postganglionic sympathetic, pain and heat, cold and pressure
State the conduction velocity (m/s), and diameter of the different nerve fiber types (different types based on conduction velocity).
Aα: 70-120 m/s and 12-20 µm Aβ: 30-70 m/s and 5-12 µm Aγ: 15-30 m/s and 3-6 µm Aδ: 12-30 m/s and 2-5 µm B: 3-15 m/s and 1-3 µm C: 0.5-2 m/s and 0.1-2 µm
What are the different nerve fibre types based on sensory function ? What is the origin of each type ? What is the equivalent of each type on the classification system based on conduction velocity ?
IA: Muscle spindles (Aα) IB: Golgi tendon organs (Aα) II: Muscle spindles; touch and pressure receptors (Aβ and Aγ): III: Pain and temperature receptors (Aδ) IV: Pain and other receptors (C)
What do alpha motor neurons innervate ?
Skeletal muscle
How many muscle fibers can one neuron innervate ?
How many motor neurons can innervate one muscle fiber?
How many motor neurons can innervate a muscle ?
Each neuron will innervate multiple muscle fibres, but each muscle fibre will only be innervated by one motor neuron
Many neurons can innervate a whole muscle (neighbouring fibres may be innervated by different neurons)
What are the components of a motor unit ?
A motor neuron and the muscle fibres it innervates.
What is the NT of motor units ?
ACh
How many muscle fibers per motor neuron do the smallest motor units innervate ?
How many muscle fibers per motor neuron do the largest motor units innervate ?
Smallest innervate 5-10 muscle fibres per motor neuron
Largest innervate ~1000 muscle fibres per motor neuron
What does the actual spectrum of motor unit sizes within a given muscle depend on ?
- The precision of control required (small motor units gives highly precise i.e. fingers, eyes)
- The force of contraction required or a low precision (large motor units ie postural muscles or calf muscles)