Topic 6: Nervous System IV Flashcards
Efferent (Motor) Nervous Systems
-Autonomic and Somatic Nervous systems
Autonomic Nervous System
CNS ⇒ smooth + cardiac muscle, glands
-2 neurons to effector (preganglionic + postganglionic)
ANS neurons can be distinguished by the type of nt released:
- cholinergic = Ach
- adrenergic = norepinephrine (NE)
Autonomic Divisions
- Sympathetic
- Parasympathetic
Sympathetic Nervous System
- function = prepares body for activity
- fight or flight response
- activated during exercise
- nt at ganglion=Ach
- nt at E=NE (except in sweat glands)
To stop chemical stimulation need to remove nt (SNS)
- ACh broken down by acetylcholinesterase (AChE) – on postsynaptic membrane (cell body/dendrites of postsynaptic cell)
- NE broken down by MAO (monoamine oxidase) ) - in synaptic end bulb of the neuron that released it
b) Parasympathetic Nervous System
- function = rest + digest
- “housekeeping”
- most organs innervated by ANS have both SNS + PSNS – usually have opposite actions
- ANS regulates internal processes continuously and automatically
e. g. heart rate ⇒ SNS excites, PSNS inhibits - nt=Ach
Effects of ANS
Organ(s): SNS (fight or flight)/PSNS (rest + digest)
- Pupils of Eyes (iris muscles): dilate/constrict
- Heart: increase heart rate (HR) & force of contraction/lower HR
- Gastrointestinal Tract: lower motility/increase motility
- Blood Vessels (smooth muscle): vasoconstriction/*no innervation of blood vessels (except penis + clitoris)
- Sweat Glands: increase secretion (cold sweat)/no innervation
- Digestive Glands: decrease secretion (except saliva)/increase secretion (all of them)
- Genitals: ejaculation (♂)/erection, lubrication (♂ + ♀)
Higher Control of ANS
Cerebrum to hypothalamus to medulla oblongata to ANS to SNS/PSNS
- hypothal. does not need cerebral input for its ANS functions, but emotions can cause autonomic effects
e. g. blushing, fainting, cold sweat, ⇑ HR etc.
Somatic Nervous System
CNS ⇒ Skeletal muscles
- 2 neurons to effector (upper motor neuron + lower motor neuron)
- 3 types of movement:
- Reflexes, voluntary, rhythmic
Reflexes
- spinal - least complex - require sensory input from e.g. proprioceptors (e.g. muscle spindles)
- postural - for balance, posture
- require sensory input from e.g. proprioceptors (e.g. muscle spindles), eyes, inner ear
Voluntary
- most complex
- no external stimuli required (act of will)
Rhythmic
- walking, running etc.
- combination of reflex + voluntary
Levels of motor control
-Level 1: Planning
-Level 2:
-Level 3:
-Level 4: Spinal Cord
-Cerebellum
-Basal Nuclei
Corticospinal (Direct) Pathway
Level 1: Planning
- do you want to want move? – If yes, what movement needed? Which muscles need to contract?
- plans sequence of muscle contractions
- signals primary motor cortex
- works with input from cerebellum
Level 2
signals directly to lower motor neurons (via corticospinal tract) – for fine skilled movements
Level 3
- brain stem nuclei ⇒ descending motor tracts ⇒ lower motor neurons (= indirect tracts)
- receive input from cortex, basal nuclei, cerebellum
- involved in co-ordination of large muscle groups for:
- maintenance of posture
- locomotion
Level 4: Spinal Cord
- contains cell bodies of lower motor neurons
- networks of neurons (central pattern generators; CPGs) which set rhythmic, repeated movements (e.g. walking, running)
- require cortical signals to begin or stop movement
Cerebellum
- role in planning + initiating movement ⇒ sends input to cortical areas
- stores planned movement + compares actual to plan, using sensory input from e.g. proprioceptors - corrects if necessary
- maintains balance, controls eye movements, and has a role in maintaining muscle tone (=low level of contraction)
- coordinates skilled voluntary muscle movements and timing of contractions involving more than 1 joint
Basal Nuclei
- aid in planning movement
- suppress unwanted motions e.g. at rest
- role in maintaining muscle tone
Corticospinal (Direct) Pathway
-cortex to skeletal muscle Parts: -Upper motor neurons -cell bodies in primary motor cortex -axons into spinal cord -Lower motor neurons -cell bodies in ventral horn of spinal cord -axons exit via spinal nerves
Clinical Applications
- Destruction of Upper Motor Neurons
- Destruction of Lower Motor Neurons
Destruction of Upper Motor Neurons
-reflex arcs still present
Get:
-Spastic Paralysis - ⇑ muscle tone (no muscle atrophy)
-Exaggerated reflexes e.g. patellar, Achilles, Babinski sign
e.g. Plantar reflex – scratch sole of foot
-normal response = planar flexion (toes curl under)
-Babinski sign = extend big toe - indicates damage to upper motor neurons (except in babies where it’s normal – corticospinal tract not yet fully myelinated)
Destruction of Lower Motor Neurons
Get:
- loss of reflex arc (no reflex)
- flaccid paralysis - ⇓ tone, marked muscle atrophy
e. g. Polio (poliomyelitis) = virus destroys cell bodies in ventral horn of sp. cord.
