Action Flashcards
How long did my guy Mike the headless chicken live and how was he fed?
Lived for 18 months from 1945- 1947 (RIP brother) and was fed with fluids and corn through a hole in his small intestine.
Also earned 4.5k (50k now) per month so he was all about the securing the bag even when headless.
In what way is the communication and translation of action in the brain the opposite of the visual system?
The hierarchical organisation of motor pathways go from ‘concept’ to muscle control
What is the final common pathway of all motor output?
The ventral horn Alpha motor neuron
What can be done to test the response of the alpha motor neuron? Describe this
The stretch reflex:
A hammer hits below the knee and stretches the quadriceps. The muscle spindles in the quadriceps femoris muscle acts as a stretch receptor and shoots a signal through the sensory neuron to the spinal cord. A signal is then sent through the alpha motor neuron causing the muscles to contract and you to kick out.
In which ‘root’ are each of these neurons located
sensory neuron- dorsal root
motor neuron- ventral root
Which parts of the spinal cord control 1) posture and 2) fine movements?
Dorsolateral part- distal muscles; fine movements
Ventromedial part; Proximal muscles; posture
Name and describe two diseases which affect the alpha motor neuron
Lou Gherig’s disease or ALS: Amyotrophic Lateral Sclerosis
Poliomyelitis: Viral infection that selectively attacks alpha motor neurons
Give an example of a constant requirement of the stretch reflex
keeping posture
What function does the gamma motor neuron carry out during voluntary movement and why?
Gamma motor neurons contracts muscle spindle during voluntary movement so that they stay ‘short enough’ to sense stretching when muscles are short
What brain area do these gamma motor neuron get input from when carrying out this function?
Pons
What two types of muscles fibres are involved in this reflex?
Larger extrafusal muscle fibres and smaller intrafusal muscle fibres within the muscle (see copy for diagrams)
What else happens when the the hammer hits the knee and stretches the quadriceps?
The reciprocal inhibition of antagonistic muscles. When extensor (quadriceps) contracts, Flexor relaxes.
Describe this reciprocal inhibition of the antagonistic muscle in 3 steps
1) Afferent impulses from stretch receptor to spinal cord via the sensory neuron. An interneuron then activates =>
2) Efferent impulses to motor neurons (serving quadriceps) cause contraction of the stretched muscle that resists/ reverse the stretch
3) Efferent impulses to antagonist muscles are damped (reciprocal inhibition) via the motor neuron serving antagonist muscle group (hamstrings)
What is meant by the crossed extensor reflex?
As one limb flexes, the other extends (walking, keeping balance when retracting your leg from standing on a pin)
However walking also utilises a different process to the crossed extensor reflex. Describe and name this process
Due to the central pattern generator, the spinal cord can do walking ‘all on its own.’ The central pattern generator ‘creates’ locomotion movements all on its pwn. The only thing that is requires in a high level ‘gait’ command (or it can be set in motion by proprioceptive feedback).
Give an example of an experiment which demonstrates this central pattern generator
A decerebrated cat (high level spinal cord cut) walks on a treadmill, in different tempos.
What other movements are fully automatic and highly coordinated in this manner? (3)
Swallowing, breathing orientating
Describe six steps which are involved in swallowing
1) When a person is not swallowing, the oesophageal sphincter muscle is contracted , the epiglottis is up and the glottis is open, allowing air to flow through the trachea into the lungs
2) The swallowing reflex is triggered when a bolus of food reaches the pharynx
2) the larynx , the upper part of the respiratory tract moves upward and tips the epiglottis over the glottis, preventing food from entering the trachea
4) The oesophageal sphincter relaxes, Allowing the bolus to enter the oesophagus
5) after the food has entered the oesophagus, the larynx moves downward and opens the breathing passage
6) Waves of muscular contraction (peristalsis) move the bolus down the oesophagus to the stomach
What is the function of the withdrawal reflex
Protecting from damage
Describe the steps involved in the withdrawal reflex
Pain receptors in the skins send an impulse through the sensory nerve (afferent nerve) to the spinal cord, where it connects to the motor neuron through an interneuron. This neuron then causes the muscles to contract and withdraw the part being stimulated
What reflex protects from overload?
Golgi tendon reflex protects the muscle from excessively heavy loads by causing the muscle to relax and drop the load
Explain the steps involved in the golgi tendon overload
=>Muscle contraction stretches the golgi tendon organ.
=>If excessive load is placed on muscle, the golgi tendon organ fires.
=> The motor neuron is then inhibited
=> The muscle relaxes
=> the load is dropped
What name is given to this type of motor control which is responsible for these reflexes, antagonistic relaxation, central pattern generators and others?
Lower motor control (because they all take place in the spinal cord)
To what extent is the actions we do carried out by the lower motor control?
They do all the ‘work.’ Only thing that is needed is a central ‘command.’ And some checks and balances…