WEEK 7 LECTURE + TUTORIAL Flashcards
movement (21 cards)
Sensory feedback to motor neurons
- Muscle Spindles
-Fibrous capsules containing specialised muscle fibres
-Detects change in muscle length
-Contracts of spindle poles to keep 1a axons within working range
-Muscle contraction
2.Golgi tendons
-Located at the junction of a muscle and a tendon
-Innervated 1b sensory axons
-Monitors muscle tension (tendon stretch)
-Muscle Inhibition
Monosynaptic Reflexes definition
serves to provide a rapid and automatic response to stimuli, typically for protective or regulatory purposes
Key Purposes of monosynaptic reflexes:
1.Quick Response: They allow for extremely fast reactions to stimuli. Since there is only one synapse between the sensory and motor neurons, the response is nearly immediate.
2.Protection: One of the most common monosynaptic reflexes is the patellar reflex (knee-jerk), which helps protect muscles and joints from overstretching by quickly contracting a muscle when it is stretched too much.
3.Postural Control: Monosynaptic reflexes also help maintain posture. For example, the stretch reflex helps maintain muscle tone and keeps us balanced when we stand or move.
4.Homeostasis: In some cases, these reflexes help regulate internal conditions like muscle tone or blood pressure.
*In short, the monosynaptic reflex pathway allows the body to react rapidly to changes in the environment, particularly in ways that protect it from injury.
Polysynaptic reflexes
Polysynaptic reflexes involve multiple synapses between neurons, meaning there are more than two neurons involved in the reflex pathway
They include one or more interneurons between the sensory and motor neurons
Key Features of Polysynaptic reflexes
1.Multiple Synapses: These reflexes involve multiple neurons and at least one interneuron between the sensory and motor neurons.
2.Slower Response: Since more neurons are involved and the signal has to travel through multiple synapses, the response time is generally slower than monosynaptic reflexes. However, the complexity of the response is greater.
3.More Complex Responses: Polysynaptic reflexes allow for more coordinated or complex actions, often involving the activation or inhibition of multiple muscles or body parts.
4.Flexibility and Integration: These reflexes can integrate information from various sensory inputs and are often modulated by higher brain centres
Examples of polysynaptic reflexes
- Withdrawal Reflex (Flexor Reflex):
-This is a protective reflex that occurs when you touch something painful, like a hot stove. The sensory neurons detect the pain and send signals to the spinal cord. Interneurons process the information and activate motor neurons that cause the muscles to contract and withdraw the body part from the painful stimulus
2.Crossed-Extensor Reflex:
This reflex occurs simultaneously with the withdrawal reflex to help maintain balance.
3.Stretch Reflex with Modulation:
While the stretch reflex is monosynaptic, it can be influenced by polysynaptic pathways for more complex control, such as in postural adjustments or balance during movement.
Purposes of Polysynaptic reflexes
Protection
Coordination
Flexibility
Cortical structures involved in the control of movement
-The Primary motor cortex (M1)
-Supplementary motor area (SMA)
-Premotor cortex (PMA)
The Primary Motor Cortex
-Involved in the execution of movement
-Organised somatotopically: motor homunculus
Supplementary motor area
-Learning and planning of behaviours consisting of sequences of movements
-Damage disrupts ability to execute well-learned sequences of responses
-Pre-SMA is associated with control of spontaneous movement
-Stimulation of SMA and Pre-SMA provokes the urge to make a movement or the anticipation that a movement will occur
Premotor cortex
-Learning and executing of complex movements
-Guided by sensory information
-Contains mirror neurons
Neurodegenerative diseases
*Two progressive neurodegenerative diseases involving the basal ganglia and characterised by motor deficits
- Huntington’s disease
- Parkinson’s disease
Huntington’s disease
-Hereditary disease caused by degeneration of the striatal neurons; loss of inhibition exerted on globus pallidus
-Symptoms: Uncontrollable jerky limb movement, impaired ability to cease movements, cognitive and emotional change
Cerebellum functions
-Part of the metencephalon, 2 hemispheres, connected to brainstem
Functions:
-Smooths and integrates ongoing movement
- Important for independent rapid skilled limb movements
- Important for postural reflexes
-Integrates movement sequences
-Partly responsible for motor learning
Cerebellum damage
Possible causes: Stroke, haemorrhage, alcoholism, tumour, physical trauma, chronic degenerative conditions
-Cerebellar Ataxia: lack of coordination of movements
-Can manifest as difficulty walking, particularly with narrow base
-Intention tremor = involuntary, rhythmic muscle contractions that occurs during a purposeful, voluntary movement
-Slow tremor of the extremities that occurs at the end of a purposeful movement (touching a finger to the tip of a nose)
-Jerky, poorly coordinated, exaggerated movements
Reticular Information
-includes a large number of nuclei in the brainstem,
-Important in a variety of moto functions:
-Regulates muscle tone
-Control semiautomatic responses
-Controls posture
-Plays a role in locomotion
2 Major descending motor pathways
- Lateral pathways
- Ventromedial pathways
Lateral Pathways
1.Originate in the cortex
-Composed of three tracts
-Lateral corticospinal (light blue)
-Corticobulbar (green)
-Rubrospinal (red)
-Control voluntary independent movement of distal muscles (forearm, hand)
Ventromedial Pathways
-Originate in the brainstem
-Composed of four tracts
-Ventral corticospinal tract
-Vestibulospinal tract
-Tectospinal tract
-Reticulospinal tract
-Controls automatic movements of proximal and axial muscles and movements related to posture and locomotion
What is Parkinson’s disease
A progressive neurodegenerative disorder which:
-Impairment of movement initiation, particularly automatic
-Affects nerve cells in substantia nigra which produces dopamine
-When 80% dopamine is lost, PD symptoms occur such as tremor, slowness of movement, stiffness, balance
Huntingtons disease vs parkinson’s causes
- Caused by a mutation of the HTT gene responsible for making the Huntingtin protein which plays a crucial role in brain nerve cells for striatal region and inhibition of globus pallidus
- Causes are mainly unknown, genetics, head injury?, aging?
