Motor control, relexes, & senses Flashcards
Efferent Nervous System
Motor control
NS uses many sensory inputs to plan motor actions
Processed consciously in the cerebral cortex
Processed unconsciously in other parts of CNS
A few senses are especially important for unconscious processing
Somatic senses
Efferent senses of the body
1. Proprioception: sense of position of limbs
2. Vestibular sense: sense of balance
Proprioception
sense of position of limbs
- Muscle spindles - in skeletal muscle organs detect stretch = length of muscle
- Gogi tendon organs - in tendons right next to muscle detect tension = force on muscle
Vestibular sense
Sense of balance
- In inner ear
- Detects position and motion of head
Premotor Complex
- Plans complex motions involving multiple muscle groups
- Receives signals from sensory cortices + association areas
Primary motor complex
- Directly controls somatic motor neurons
- Has a homunculus = map of the body
- Receives signals from premotor cortex
Cerebellum
Helps generate smooth + coordinated motions
- Compares motor complex plan to what is actually going on
- Gets signals from the motor cortex
– Somatic senses - especially proprioception + vestibular sense)
- Sends signals back to the motor cortex
Basal ganglia
Helps coordinate motor actions by receiving signals from all parts of the cortex, then sends signals back to the premotor complex.
At default, it suppresses cortex from generating motions
Most release suppression to move.
Giant Pyramidal Neurons
- Cells bodies are in the primary motor complex
- Axons goe down the spinal cord
- Synapse on somatic motor neurons in the spinal cord
- Contains Pyramidal Tracts
Pyramidal Tracts
White matter tracks that pyramidal axons travel down
Ventral
Direct = go directly from cortext to motor neurons
Structures of Motor Control
in the Efferent Nervous System
- Premotor cortex
- Primay motor cortex
- Cerebellum
- Basal Ganglia
- Giant Pyramidal Neurons
- Pyramidal tracks
- Motor neurons that leave CNS & make muscles contract
Reflex
Definition + Types
= An automatic (unconscious) response to a stimuli
- Faster than conscious thought
- Conscious thought can overcome reflexes
Reflex Types:
- Autonomic
- Somatic
- Pollysynaptic
- Monosynaptic
- Short
- Long
Reflex Arc
Series of neurons that a reflex passes through
Receptor = detects the stimulus
1. Signals the Afferent neuron = carries the signal from receptor to integration center
2. Integrating center = processes information about the stimulus + makes decisions
3. An efferent neuron = carries the signal from integrating center to effector
4. Effector gets signal from efferent neuron + does something (ex: muscle contraction)
Autonomic Reflex
= efferent neurons are autonomic + effector for smooth muscle, cardiac muscle, glands or adipose
Somatic Reflex
= efferent neurons are somatic motor neurons + the effector is always skeletal muscle
Short Reflex
Initiated by the integrating center in PNS
Only autonomic or visceral
Long Reflex
Integrating center in CNS
- Autonomic or somatic
- Somatic have to be long because the cell bodies are in the CNS
Monosynaptic Reflex
= reflex with only 1 synapse
- Afferent neuron synapses directly on an efferent neuron
- The integration center is synapse + decision by efferent neuron to have AP
Polysynaptic Reflex
= reflex with more than 1 synapse, have at least 1 interneuron between the afferent + efferent neuron - that creates multiple synapses
What reflexes do the brain stem control?
Complex somatic reflexes:
- Breathing
- Maintaining balance + posture
- Responding to visual + auditory stimuli
- All polysynaptic
Indirect pathways
= white matter tracts in the spinal cord
- Neurons with cell bodies in the brain stem
- Axons travel down the spinal cord in indirect pathways
- Neurons synapse on interneurons in the grey matter of the spinal cord
- Interneurons synapse on somatic motor neurons
Spinal Reflexes
Definition + Types
- Somatic reflexed
- Integration center in the spinal cord
- Monosynaptic or polysynaptic
- Synapses in the gray matter of the spinal cord
Types of spinal reflexes: - Stretch reflex
- Tendon reflex
- Flexor reflex
- Crossed-extensor reflex
Stretch reflex
When muscle is stretched, it contracts in response (as a reflex)
Initiate the reflex by hitting a tendon:
1. Muscle spindle in muscle detects stretch
2. Sends signal to spinal cord on an afferent motor neuron
3. In spinal cord afferent neurons synapse on the monosynaptic motor neuron for the same muscle
4. Efferent motor neuron carries signals to muscle that was stretched + signals the muscle
5. Muscle contracts
Reciprocal Inhibition
The antagonist to the stretch reflex that makes the other muscles relax for the flex to occur.
Polly synaptic
Afferent neuron synapses on an interneuron
The interneuron inhibits the motor neuron + on the antagonistic muscle
Tendon Reflex
When the body detects increased tension on muscle and makes the muscle relax
- So muscles don’t have too much force (they’ll damage)
- Golgi tendon organ detects tension
- Polysynaptic Spinal reflex
- Reciprocal activation occurs at the same time
ex: patellar test
Reciprocal Activation
Make the antagonists contract during a tendon reflex.
Flexor Reflex
= withdrawal reflex
Limb pulls away from painful stimulus
Can consciously overcome
Nociceptors detect pain → send signal to the spinal cord → Flexors in the limb contract + makes the extensors in the limb relax → makes you pull the limb away
Crossed-extensor reflex
Similar to a flexor reflex but you’re prevening falling over when you withdraw the other leg. This only occurs in the legs.
Have flexor reflex in one leg - opposite leg has extensor reflex: extensions contract + flexors relax
What autonomic reflexes does the brain stem control?
- Cardiovascular center
- Respiratory centers
Neurons in the brain stem synapse on presynaptic neurons in the brain stem + spinal cord
Sensory receptor
cell that responds to a stimulus + turns it into a signal in the nervous system
Afferent neuron types
- with free nerve endings
- with accessory structures
Specialized receptor cell
Cell that detects stimulus but isn’t a neuron
Membrane depolarizes
No AP, just graded potential
Signals a neuron with neurotransmitter
Sight, hearing, balance, taste, 1 touch receptor
Neuron with free nerve ending
Dendrites that detect stimulus and don’t have anything around them
ex: Temperature, pain, smell
Neuron with accessory structures
Tissues are around dendrites that aid in the detection of stimulus
ex: Mostly touch + proprioception
Special Senses
Senses with their own specialized organ: Smell, sight, hearing, balance, taste
- Have specialized receptor cells (except smell)
- Afferent neurons are bipolar (except taste)
- Travel to the brain on special cranial nerves (except taste)
- Each one had their own dedicated sensory area of the cortex
Only senses with bipolar neurons
Everything else is pseudounipolar
Somatic Senses
Senses of the skin, muscles, and joints: Temperature, pain, proprioception, touch
- Receptors are afferent neurons (except 1 touch receptor)
- Afferent neurons are pseudounipolar, cell bodies are in the dorsal root ganglion
- Travel on all spinal nerves + most cranial nerves
- Perceived all in the somatic sensory cortex
Visceral Senses
Senses of internal organs + fluids in the body: pH or O2 or CO2 in blood, illness, fullness, visceral pain (not totally consciously aware)
-Afferent neurons are pseudounipolar
- Enter the CNS on spinal nerves: glossopharyngeal (IX), vegas nerve (X)
Chemoreceptors
Detect chemicals in and out of the body
Smell, taste, CO2 or O2 in blood, sugar in blood, what’s in the digestive tract
Almost all have protein receptors in the plasma membrane
Mechanoreceptors
Detect physical pressure
Mechanically gated ion channels open when there is pressure on the cell
Touch, proprioception, hearing, balance, blood pressure
Thermoreceptors
Respond to temperature
Have specialized ion channels that open up at certain temperatures
Different channels open at different temperatures
Responds to chemicals (spicy)
In skin, muscle, viscera, hypothalamus
Photoreceptors
Respond to light
Only in the retina of the eye
Sensory Transduction
How a neuron turns a signal from a stimulus to a signal in the nervous system.
Receptor potential
Membrane potential in a sensory receptor
- Stimulus changes the receptor potential
- Change in potential proportional to the strength of stimulus
- Ion channels open + close in response to stimulus (except salt)
Receptive field
Place where receptor detects stimulus
Each receptor has its own field:
Touch receptor - location on skin
Photoreceptor in eye - light that reaches certain part of the retina
Nervous system knows where stimulus comes from by which receptor was activated
Size vs precision of receptive field
Large receptive field needs fewer receptors - less precise
Small receptive field needs more receptors - more percise
Sensory Modality
A type of stimuli you detect
Light, sound, pressure on skin, smell
Sensory quality
Differences between what we perceive in stimuli of same modality:
Light → color Sounds → tone Smell → different smells
Touch → light vs deep Temperature → hot vs. cold
Different receptors detect stimuli of different modalities + qualities
Nervous system knows what type of stimulus based on which receptor is detected
What are the 2 ways receptors can encode the size of stimulus?
- Bigger stimulus → higher AP frequency
- Bigger stimulus → activates more receptors
Adaptation
Many receptors stop responding to a stimulus the longer it goes on for
Tonic receptors
Fire APs repeatedly during a stimulus
- Frequency of AP will decrease as stimulus goes on
- Slow adaptation
Phasic receptors
Signal AP when stimulus starts + stops
- Not while it’s going on
- Fast adapting
Labeled line coding
Each receptor travels to the CNS on a single tract/ line
- CNS knows what receptor a signal comes from because it knows what line it comes from
- Tells CNS modality, quality, + location of the stimulus
Sensory Pathways
The route a signal takes from receptor to the brain
Cortical Map
Touch Receptors
Detect pressure on skin + other places
Mechanically gated ion channels
When membrane is pushed on → Pulls ion channels open →Membrane depolarizes
Merkel cells
Specialized cells in the stratum basale that detect light touch
Merkel nerve endings
Afferent neurons with free nerve endings that are signaled by merkel cells
Tactile corpuscles
Small neurons with accessory structures that detect light touch under the epidermis, in the dermal papillae.
Common in hairless skin
Dendrites are wrapped with Schwann cells
Lamellar corpuscles
Big + deep in the dermis to detect deep touch and vibrations.
A sensory neuron with accessory structure and many layers of collagen around its dendrites.
Bulbous corpuscles
Neurons with accessory structures to detect deep prolonged touch + skin stretching.
Elongated connective tissue capsules around dendrites
Thermoreceptors
Pseudounipolar afferent neurons with free nerve endings that detect temperature.
Their specialized channels only open at certain temperatures + chemicals
Hot + cold have different receptors and travel on separate labeled lines (Hot receptors are deeper in the dermis)
Nociceptors
Neurons found everywhere with free nerve endings that detect pain
Responding to cell damage:
- Cells release chemicals when damaged
- Nociceptors detect chemicals
- WBCs can trigger nociceptors when they detect damage
Also respond to noxious stimuli
Information goes to the CNS or bipasses to other tissues
Noxious Stimuli
Things that can hurt you
- Really high or low temps
- Strong forces
- Certain chemicals (acids)
Visceral pain
Pain that you feel in visceral organs but don’t perceive as well as other parts of the body. Could be reffered pain.
Referred pain
= Experience visceral pain in other places in the body than where the injury actually is
Causes nociceptors from both places travel on the same neuron
Ex: heart attaches - feel on the medial size of the L arm
Itching
Itch receptors are pseudounipolar with free nerve endings that respond to chemicals that stimulate inflammation - histamines
What roll do muscle spindles play in prorioception?
As a major receptor to detect stretch/ changes in length in skeletal muscle
Intrafusal fibers in
- Muscle is stretched, intrafusal fibers (in connective tissue capsul) stretch + pull together, that stimulates the afferent neurons
- Fibers stimulated to contract at the same time as muscle
- Muscle spindle gets shorter
- Remains tight as the muscle contracts
Intrafusal fibers
Muscle cells inside the connective tissue capsule of muscle spindles with afferent neurons wrapped around. Contract at the same time as muscle when stimulated.
What roll do golgi tendon organs play in proprioception?
As a major receptor in tendons with neurons wrapped around its collagen fibers and surrounded by capsul.
Muscle contracts → collagen fibers pull together → stimulates neuron
Joint Receptors
Are found around joint capsules to detect how bent a joint is
Associated structures: lamellar + bolbous corpuscles, gogi organs, nociceptors
First Order
Neurons
Path to pain
Pseudounipolar sensory neurons that enter the spinal cord on the dorsal root or brain stem.
- Branches in the spinal cord
- Some branches synaps on neurons in the spinal cord for reflexes
- Some branches synapse on second order neurons in the spinal cord or the axons of first order neurons that can travel up the spinal cord and synaps in the brain stem
Second Order
Neuron
Stimulated by first order neurons then go the thalamus and stimulate third order neurons
Third Order
Neurons
Start in the thalamus then signal cells in the somatosensory cortex
Some signals go directly to the cerebellum, bypassing the thalamus
Somatosesory cortex
Where you perceive all your somatic senses on the post central gyrus
= both homunculus
