Motor 1 Flashcards
Skeletal muscles ___ at the ___ to move bones
Pull at the tendon
Types of muscle
- Striated: skeletal (we focus on this!), cardiac
- Smooth muscle (in your organs, innervated by autonomic nervous system)
Classifications of muscles by contraction
- Flexors
- Extensors
- Agonists/synergists
- Antagonists
Diagram of flexors and extensors
Flexors
Flexion at the joint (e.g. bicep)
Extensors
Extend at the joint (e.g. triceps)
Agonists/synergists
Muscles that contract together (e.g. biceps and brachialis)
Antagonists
- These are the muscles working against agonists (e.g. triceps oppose biceps)
- While agonists contract, antagonists relax to create smooth movement
Anatomical classifications of muscle
- Axial muscles: move trunk, maintain posture
- Proximal/girdle muscles: move shoulder, pelvis, elbow, knee; locomotion
- Distal muscles: move hands, feet, digits; fine motor skills, specialized in humans
Fast twitch (white) muscle
- High contraction force, rapid fatigue
- High level of stored energy
- Low mitochondrial density, use anaerobic metabolism
- Low capillary density and blood supply
- Used for sprinting
- Force increases rapidly, peaks at a higher level, and diminishes rapidly
Slow twitch (red) muscle
- Lower contraction force, slow fatigue
- Low level of stored energy
- High mitochondrial density, use aerobic metabolism
- High capillary density and blood supply
- Used for endurance exercise/continuous use of muscle (e.g. neck muscles)
- Longer time for force to be generated, peaks at lower level, generated force lasts longer
Composition of fast and slow twitch muscle
- Different muscles have different compositions of muscle fiber types (soleus - posture control and endurance, all slow; gastrocnemius - mixed function, both fast and slow)
- Different people have different compositions of muscle fiber types (genetics, training can change this slightly)
- Motor neuron innervation determines whether a muscle fiber is fast/slow
The spinal cord sends motor neuron axons to the brain through the ___
Ventral horns
Describe the enlargements of the ventral horn in certain parts of the spinal cord
- The cervical and lumbar segments have enlargements due to extra gray matter (cell bodies) needed for fine motor control
- Cervical enlargement: arms/hands/digits
- Lumbar enlargements: legs
Organization of the spinal cord
- Lateral ventral horn controls lateral muscles (e.g. hands)
- Medial ventral horn controls medial muscles (e.g. torso)
- Neurons innervating flexors are more dorsal to neurons innervating extensors
Neurons innervating flexors are more ___ to neurons innervating extensors
Dorsal
The lateral ventral horn controls ___ muscles, e.g. ___
Lateral muscles, e.g. hands
The medial ventral horn controls ___ muscles, e.g. ___
Medial muscles, e.g. torso
What is the basic unit of muscle?
Muscle fiber/muscle cell
Where do muscle fibers get input from?
From only one alpha motor neuron at the neuromuscular junction
What neurotransmitter does the neuromuscular junction use?
ACh
At the neuromuscular junction, the alpha motor neuron synapses on the muscle fiber at the ___
Motor end plate
Neuromuscular junction
- Gets input from only one alpha motor neuron (AKA lower motor neuron) at NMJ
- Very fast, very reliable – each AP always generates an AP in the muscle fiber
- Uses ACh as neurotransmitter
- Synapses on the muscle fiber at the motor end plate
Motor Unit
- 1 alpha motor neuron (αMN) and all the muscle fibers it innervates
- 1 muscle fiber gets input from 1 αMN, but 1 αMN can innervate many muscle fibers
- Smaller motor unit = less muscle fibers per αMN = finer control, more precise
- Each motor unit contains muscle fibers of the same type
- αMN determines fast/slow twitch type