Motor Flashcards
main properties of somatic motor pathways
Activity can be voluntary or involutary (i.e. reflex)
Single-Neuron Pathway: from the (CNS) to the effector organ (skeletal muscle), without synapses in peripheral ganglia.
Neurotransmitter: ACh released at the neuromuscular junction + nicotinic ACh receptors
Effect: Always excitatory i.e. make muscle contract (voluntary movement)
No Ganglia: There are no ganglia or synapses outside the CNS in somatic motor pathways.
main properties of autonomic motor pathways
Involuntary Control: control smooth muscle, cardiac muscle, and glandular tissue and operate involuntarily, without conscious control.
Two-Neuron Pathway: a preganglionic neuron that extends from the CNS to a ganglion, and a postganglionic neuron that extends from the ganglion to the effector organ.
Neurotransmitters: parasympathetic (pre) and sympathetic pathways (pre post) release ACh/ + postganglionic sympathetic fibers release noradrenaline. (for the adrenal sympathetic pathway = chromaffin cells release catecholamines : adrenaline/noradrenaline into the bloodstream)
Effect: physiological functions, including heart rate, digestion, respiration, and glandular secretion, often in response to internal or external stimuli.
Presence of Ganglia: Autonomic ganglia are present outside the CNS between preganglionic and postganglionic neurons (where synpases are). (no ganglia for the adrenal sympathetic pathway = adrenal medulla acts as ganglion)
List the key components of a neural reflex
Receptor: detects a stimulus and converts it into a nerve impulse.
Sensory Neuron (Afferent Pathway): carries the nerve impulse from the receptor to the central nervous system (CNS)
Integration Center: In the CNS, the nerve impulse is processed and integrated.
* spinal reflexes do not require input from the brain
* cranial reflects are integrated within the brain
Motor Neuron (Efferent Pathway): processed nerve impulse is transmitted along a motor neuron carried to the effector organ, typically a muscle or gland.
* somatic motoro neurones control skeletal muscles
* autonomic neurones control smooth and cardiac muscle, glands and adipose tissues
Response: The effector organ responds to the nerve impulse by producing an action
Types of reflex pathways
1. monosynaptic : one afferent and one efferent (only somatic motor reflexes can be monosynaptic)
2. polysynaptic reflexes : one or more interneurons between the afferent and efferent. (all autonomic are polysynpatic because they have three, one afferet and two efferent)
Describe the key components of a skeletal muscle reflex
- monosynaptic reflex
- polysynaptic reflex
–> somatic motor reflex has both synapses in the CNS and an interneuron
That’s a great summary! To add a bit more detail:
- Proprioceptors: sensory receptors located within the muscle and tendons that detect changes in muscle length and tension, as well as the position of joints –> send feedback to CNS
- Central Nervous System (CNS) Integration: sensory information processed in the CNS
- Alpha Motor Neurons: sends motor commands via alpha motor neurons to the skeletal muscle.
–> These motor neurons innervate the extrafusal muscle fibers == responsible for muscle contraction.
a motor unit
Motor Neuron + Muscle fibers
one muscle may have many motor units of different fibre types
alpha motor neurons
somatic motor neurones that innervate skeletal muscle contractile fibres
types of proprioceptors
proprioceptors sensory receptors that provide feedback to the central nervous system (CNS) about the position, movement, and tension of muscles and joints. 3 main types:
Joint Receptors:
* Found in the joint capsules and ligaments surrounding joints.
* Detect changes in joint position, movement, and direction.
Muscle Spindles:
* embedded within skeletal muscle.
* Consist of intrafusal muscle fibers
* Detect changes in muscle length (stretch) and the rate of change in muscle length (velocity).
Golgi Tendon Organs (GTOs):
* Located at the junction between muscle fibers and tendons.
* Detect changes in muscle tension or force (muscle contraction).
differentiate between Golgi tendon organs (GTOs) and muscle spindles:
Structure:
* Golgi Tendon Organs: links the tendon with the muscle, composed of sensory nerve endings intertwined within collagen fibers of the tendon.
- Muscle Spindles: Embedded within skeletal muscle, consisting of intrafusal muscle fibers surrounded by a connective tissue capsule.
Function:
- Golgi Tendon Organs: Respond to changes in muscle tension or force, particularly during active muscle contraction.
- Muscle Spindles: Detect changes in muscle length (stretch) and the rate of change in length (velocity).
golgi tendon bodies
When muscle contraction pulls on the collagen fibers of the tendon, the tension is transmitted to the Golgi tendon organs.–> Golgi tendon organs are stimulated, leading to the firing of sensory neurons associated with them = transmit signals to the central nervous system (CNS), specifically to the spinal cord.
This then signals the motor neurons to innervate the extrafusal muscle fibers (regular muscle fibers responsible for contraction) of the muscle undergoing tension.
As a result, the muscle contracts and pulls on the tendon, causing it to tighten further.
muscle spindles
are sensory receptors located within skeletal muscles that respond to changes in muscle length or stretch.
–> composed of specialized muscle fibers called intrafusal muscle fibers, which are embedded extrafusal muscle fibers
==> these fibres lacking myofibril in the central region so they are non-contractile (non-contractile region of intrafusal muscle fibers is wrapped with sensory nerve endings)
==> ends of intrafusal muscle fibers have myofibrils and are contractile, similar to extrafusal muscle fibers.
–> sensory endings are sensitive to changes in muscle length or stretch.
When the muscle undergoes stretch, these sensory nerve endings are stimulated and travel to the CNS
–> gamma motor neurons from CNS innvervate the intrafusal muscle fibers and cause contraction of these fibres.
stretch reflex
load added –> stretches the muscle
1. sensory information directly synapses onto spinal cord and then appropriate alpha motor neuron
2. alpha motor neuron allow muscles to contract
3. contraction protects the muscle to prevent overstretching
3. firing rate of afferent sensory neuron decreases (negative feedback)
alpha gamma coactivation
alpha motor contract extrafusal fibres
gamma motor innervate contractile ends of your intrafusal muscle fibres
–> silmutaenous = co-activation
* muscle + intrafusal fibres both contract
patellar reflecx
- monosynaptic reflex
–> stimulus = tendon stretches
receptor : muscle spindle stretches
1. sensory neuron receives signal from receptor
2. afferent pathway and sensory neuron synapses in spinal cord
3, along alpha motor neuron to contract quadricep muscle == swing leg forward
3. SILMUTANEOUSLY : inhibitory interneuron to relax antagonist muscle (hamstring)
=> hamstring relaxed for leg to lengthen
Flexion & Crossed Extensor Reflexes
remove limb from painful stimulus
1. painful stimulus –> primary afferent neuron takes it to spinal cord
lifts one leg up, quad contracts and hamstring relaxes, vice versa on the other leg
* need to retain balance on contralateral side
integration of reflexes
- signal come in to stimulate sensory receptors –> spinal cord
- spinal cord = direct output
- motor cortex controls execute = alpha motor neurons
