innervate both spindles and skeletal muscle

Provide increased surface area to hold nicotinic receptors on the myocyte.

Can be diminished to provide less nicotinic receptors, less chance of an endplate potential

1. Ach released

2. Nicotinic receptors in NMJ bind Ach, causing Na+ influx, Action Potential

3. Action Potential Propagates to transverse tubule, where Ca+ channels are activated

4. The depolarization causes Ryanodine receptors in sarcoplasmic reticulum to release Ca+ into the cytoplasm of the myocyte

5. Ca+ binds troponin, uncovering myosin binding sites

6. Myosin hydrolyzes ATP to ADP, forms a crossbridge with actin, creates a power stroke

7. Calcium is released, actin relaxes

Aerobic, mitochondria, fatigue resistant

(Type 1 muscle Fibers)

Attatch to Type S motorneurons

Anaerobic, use glycogen, produce lactic acid

(Type 2a and 2b)

Innervated by Type FR and FF motor units

slow twitch, small force, high resistance to fatigue, innvervate type 1 fibers

small cell bodies, easy to depolarize, steady firing rates, postural support (skeletal muscle)

fast twitch, moderate force, somewhat fatigue resistant, innervate 2a muscle units, which have both aerobic and anerobic mechanisms

Fast powerful movements, Large Cell bodies and arbors, Depolarize slowly, fast firing rates

fast twitch, highest force, fatigues easily, innervates type 2b muscle fibers, which have anerobic mechanisms mainly.

Fast powerful movements, Large Cell bodies and arbors, Depolarize slowly, fast firing rates

Encapsulated fiber bundles that lie parallel to muscle fibers, allow for proprioception of muscle length, as the ends of the spindles move with the stretch of the muscle.

Increases firing rate as it stretches.

Have both sensor and motor innervation (to adjust spindle length, gamma motoneurons primarily)

A muscle spindle detects a change (type 1a)

Spindle transmits to spinal cord exciting motoneurons of stretched muscle, and also synergistic muscles, but inhibit antagonists 

(knock on knee test)

encapsulated receptors embedded in tendon-muscle junction, sensitive to forces from muscle contraction against a load

innervated by type 1b afferents

Relay sensory input from the periphery

Relay and modulate descending brain signals

Form networks to control reflexes, patterned behavior, movement

Receive excitatory input from collateral motoneurons, and inhibit the same collateral motorneurons (recurrent inhibition)

Inhibit the inhibitory interneurons of antagonists, net excitation

Feedback loop that keeps muscles from becoming spastic

Raise leg after stepping on glass

nociceptive neuron -> interneuron -> excite flexors on the side with the pain, but excites extensors on the side without the pain

Stabilizes the other leg as you raise your foot with a piece of glass.

Divergence to enhance neural response

Receives input from Golgi tendon organ, joint and skin afferents, and descending brain input (modulates sensitivity)

inhibits other motorneurons that innervate the same tendon. Causes relaxation when muscle is relaxed, and excitation when the muscle is moving.

Convergent input -> complex behavior

r

Plan and execute voluntary movement

Maintain Posture and Balance

Sensorimotor integration

M1 -> Execution

Premotor-> planning

Both receive sensory inputs, but mostly premotor

Both can project to motor neurons, but mostly M1

corticomotorneurons

Found mostly in primates, make monosynaptic connections with motoneurons, located in layer V of cortex, buried in the central sulcus

the SpikeTA is the average stimulus preceding a spike. Provides an idea of a recptive field.

Stimulus triggered averaging is the average spike waveform.

Control goal directed limb movements (reach to grasp). Can alter outputs to compensate for injury.

The lateral tract arises from the lateral vestibular nucleus, descends ipselaterally.

The medial tract arises form the medial vestibular nucleus and descends bilaterally, in the medial longitude fasciulus.

Lateral 

From the medulla, descends bilaterally in the ventrolateral region of the spinal cord.

Medial

From the caudal pins and dorso-rostral medlla, descends ipsilaterally in the ventomedial region of the spinal cord.

What does the reticulospinal system do?

Control voluntary reaching movements, bilateral movements, stabilize posture.

reticulospinal neurons can target the same motor neurons as the reticulospinal neurons.

They touch many things.