Nerve and muscle Flashcards
What does the central nervous system consist of?
Brain, spinal cord, (neurons and glia x2)
What does the peripheral nervous system consist of?
Peripheral nerves, neurons and glia
What do dendrites do?
- Receive input
- Send info to cell body
What do cell bodies of neurons do?
- Contains nucleus and organelles
- Sums input
What does an axon do?
- Carries electrical impulses
- May or may not be myelinated
What does an axon terminal do?
- End (terminus) of the axon
- Neurotransmitter release
Input zone
- Dendrites and cell body
- Receives chemical signals from other neurons
Summation zone
- Axon hillock
- Decision to transmit signal further
Conduction zone
- Axon, may be quite long
- Carry electrical signals between brain areas, to and from spinal cord, or to and from peripheral sensory receptors
Output zone
- Axon terminals
- Contact with input zone of other neurons
- Release of neurotransmitter = chemical signal
What does an axon hillock do?
Makes decision about whether or not to pass on information
Multipolar neurons
Multiple processes emanate from the cell body
Bipolar neurons
Two processes emanate from the cell body
Unipolar neurons
- One process emanates from the cell body
- Then branches into dendrites and axons
Anaxonic
- Axonless
- No distinct axon
- All processes look alike
Astrocytes
- Supply nutrients to neurons
- Ensheath blood capillaries
- Transmit information
Mircroglia
- Immune cells of the CNS
- Engulf microorganisms and debris
Ependymal cells
- Line fluid fulled spaces of the brain and spinal cord
- Have cilia (hair-like processes) to circulate CSF
Oligodendrocytes
- Support nerve fibres
- Ensheath them with myelin
PNS glia
- Support peripheral nerve fibres
- Ensheath them woth myelin
- Similar to oligodendrocytes (CNS)
What is myelin?
Lipid wrapped around axon
What does myelination do?
Increases conduction velocity
Afferent
Information that goes into the brain
Efferent
Response that comes out of the brain
Somatic efferent (motor)
Voluntary muscle control
Somatic afferent (sensory)
Sensory information we are aware of
Autonomic
The stuff we are not aware of and have no control over
Autonomic efferent (motor)
Involuntary muscle control
Autonomic afferent (sensory)
Sensory information that we don’t know about
Upper motor neuron
- Cell body in brain
- Axon in spinal cord
Lower motor neuron
- Cell body in spinal cord
- Axon in spinal nerve
Effectors
Skeletal muscle fibres
Neuron 1 between brain and effector
- Cell body in brain
- Axon in brain or spinal cord (CNS)
Neuron 2 between brain and effector
- Cell body in brain or spinal cord (CNS)
- Axon in PNS
Neuron 3 between brain and effector
- Cell body in CNS
- Axon in PNS
Sympathetic
Prepares body for acute/stress responses
Parasympathetic
Prepares the body for restful situations
Sympathetic chain ganglia
Place where preganglionic (neuron 2) axons synapse
What is an action potential?
The basis of all neuronal communication. They are like electrical impulses
What creates membrane potential?
The distribution of ions
What is the resting membrane potential?
-70mV
Absolute refractory period
A second action potential can not be initiated no matter how large the stimulus is
Relative refractory period
Immediately after the absolute refractory period, the initiation of second action potential is inhibited but no impossible
What is the nodes of ranvier?
Gaps in between myelination to increase conduction
Temporal summation
If stimuli occur one after the other, they are more likely to create an action potential
Spatial summation
If two or more stimuli reach the neuron at the same time, they will summate together so it’s more likely to create an action potential
Synaptic transmission
Making connections
How many segments do spinal cords have?
31
Cauda Equina
Spinal nerve roots distal to the tip of adult spinal cord
White matter
Regions in the CNS that are dominated by myelinated axons
Gray matter
Areas in the CNS that are dominated by neuron cell bodies, neuroglia and unmyelinated axons
Meninges
Protective covering for the brain
What are the three layers of meninges
- Dura matter
- Arachnoid
- Pia matter
Dura mater five features
- Outer
- Dense and fibrous
- Two layers
- Space between the layers forms venus sinuses
- Inner layer forms the dural folds
Dural folds three features
- Formed from inner layer of dura mater
- Seperate major divisions in the brain
- Provide stability of the brain within cranium
Falx cerebri
- Seperates cerebral hemispheres
- Median plane
Falx cerebelli
- Seperates cerebellar hemispheres
- Median plane
Tentorium cerebelli
- Seperates the cerebrum from the cerebellum
- Horizontal plane
Venous sinus three features
- Located where the two layers of dura mater seperate
- Collecting veins
- They collect venous blood from the brain, ‘old’ CSF after it has cycled through the ventricular system
What is arachnoid mater
Layer beneath the dura mater
Arachnoid mater five features
- Layer beneath the dura mater
- layer above the pia mater
- Does not extend into sulcui
- Contains 2 features - subarachnoid space, arachnoid granulations
- Contains blood vessels
Special features of arachnoid mater
Subarachnoid space
- Between the arachnoid and the pia mater
- Filled with cerebrospinal fluid
Arachnoid granulations
- Perforate the inner layer of dura mater
- Transport ‘old’ CSF from subrachnoid space into venous sinus
Pia mater four features
- Inner layer of the mninges
- Transparent and delicate
- Blood vessels in achnoid sit on top of pia mater
- Adheres to brain and follows gyri and extends into sulci
The ventricular system four features
- Network of interconnected spaces within the brain
- Filled with cerebrospinal fluid, which nourishes and protects the brain
- Spaces lined with ependymal cells, which circulate the CSF
- CSF is produced by the choroid plexus
Lateral ventricles
- Two of them
- One in each cerebral hemisphere
Third ventricle
Located in the diencephalon
Cerebral aqueduct
- Connects 3rd ventricle to the 4th ventricle
- Located in the midbrain
Fourth ventricle
Located at the level of the cerebellum
Cerebrospinal fluid (CSF) four features
- Surrounds the CNS
- Provides support and cushion
- Transports nutrients and waste
- Produced by choroid plexus within the ventricles
Four lobes of the brain
- Frontal lobe
- Parietal lobe
- Temporal lobe
- Occipital lobe
Frontal lobe functions
- Language
- Personality
- Motor control
Parietal lobe
- Somatosensory
Occipital lobe
- Vision
Temporal lobe
- Memory
- Hearing
Central sulcus
Separates frontal and parietal lobes
Lateral sulcus
Separates temporal lobe from frontal and parietal lobes
Parieto - occipital sulcus
Separates parietal and occipital lobes
Transverse fissure
Separates cerebrum from cerebellum
What does the cerebellum do?
Coordinating the body and cerebrum
What does the brain stem consist of?
- Mid brain
- Pons
- Medulla oblongata
What are the three types of white matter?
- Commissural tracts
- Projection tracts
- Association tracts
Neurotransmitter for somatic efferent (motor) division
Acetylcholine (ACh)
What horn of the spinal cord are somatic motor neurons in?
Ventral
What horn of the spinal cord are the autonomic motor neurons in?
Lateral
What root ganglion are the cell bodies of sensory neurons in?
Dorsal
What would happen if there was damage to the dorsal nerve root?
- Loss of sensation on same side of regions supplied with this spinal nerve.
Commissural tracts
Axons cross from side to side; both directions
Projection tracts
Axons extend between cortex and other CNS areas outside cerebrum
Association tracts
- Axons on the same side within cerebral cortex
- Communication between brain areas - short or long distance
Primary motor cortex
Execution of movement
Upper motor neuron (neuron #1)
- Cell body in primary motor cortex (precentral gyrus)
- Axon extends from motor cortex to spinal cord on opposite side
- Makes synapse on lower motor neuron
Lower motor neuron (neuron #2)
- Cell body in ventral horn (grey matter) of spinal cord
- Axon extends out of spinal cord (ventral root) into body
- Makes synapse on skeletal muscle
Damage to the primary motor cortex
Muscle weakness and paralysis in region of body corresponding to the location of damage
Spinal reflexes
- Organised neural circuit
- Usually contained within spinal cord
- Reproducible, automatic response to a particular stimulus
Process of spinal reflexes
- Stimulation of a receptor
- Activation of a sensory neuron
- Information processing in the CNS
- Activation of a motor neuron
- Response of a peripheral effector
Summation
The more local potentials occurring at the dendrites, the more likely the axon hillock will ‘decide’ to propagate the depolarisation
What is a muscle spindle formed of
Intrafusal fibres found deep in skeletal muscle
Withdrawal reflex
Often caused by painful stimulus
What is ‘turned off’ during a withdrawal reflex
An inhibitory neuron
Motor unit recruitment
Activate more motor units which increases the possible amount of contraction
What is a motor unit
A motor neuron and all the muscle fibres it innervates
Stimulation frequency
The more frequently one motor unit is stimulated, the greater the tension produced by that motor unit over time
What happens if a motor unit is stimulated frequently?
Muscle doesn’t have time to relax and tension stays high
Planning for movement
- Decision in frontal lobe sent to pre-motor cortex
- Information is sent to basal nuclei and cerebellum
- Cerebellum helps to organise contractions of muscles in response to what is happening in environment
Performing movement
- Primary motor cortex sends information to LMN
- Sensory input of many kinds of feedback to cerebellum
- Pre-motor cortex and cerebellum feedback to primary motor cortex - comparing intended with actual movement
- Primary motor cortex adjusts movement and activates again
Role of the cerebellum
- Coordinates muscles
- Compares intended movement with actual
- Helps maintain posture and gaze
- Helps learn and automate movements
- Monitors balance and maintain equilibrium and adjusts upper motor neuron activity
Drunken gait
Cerebellar deficits can cause ataxia characteristic
Special sense of CNS
- Vision
- Hearing
- Taste
- Smell
- Balance
Somatic sense of CNS
- Touch
- Pain
- Warm and cold
- Body position
What are all sensory neurons?
Unipolar
What are somatosensory sensors?
Sensory endings of an afferent neuron
What do special senses have?
Specialised receptors which synapses into an afferent neuron
4 types of information that describe a sensory stimulus
Modality, intensity, duration, location
Modality
Type of sensory receptor activated
Intensity
- Frequency of action potential firing in afferent neuron
- Relies on action potential frequency
- Greater the intensity of the stimulus, the more action potentials produced
Duration
Duration of action potential firing in afferent neuron
Location
Location of sensory receptor activated
Proprioception
- Sensation of body position
- Movement and posture
- Maintained by muscle spindles through monitoring muscle length
Touch
- Many different receptors
- Helps to contribute to proprioception
- Can tell smooth from rough, moving from still, hard from soft
Stimulus duration
- Sensory receptors are most sensitive to change
- Often show adaptation
- Frequently repeated stimulus = more action potentials
Receptive field
Region in which a stimulus can lead to activity in a particular afferent neuron
What size field in a receptor field will give good discrimination?
Small
Integration
- Cerebral cortex
- Conscious sensation and perception
Afferent neurons
- Peripheral nerve
- Tract or pathway
Sensory receptor
Sensory stimulus converted into action potentials
Sensation
- Conscious identification of ‘what’ and ‘where’.
- Primary region of cortex
Perception
- Meaningful interpretation of sensation
- Secondary region of cortex
Somatotopic organisation
Areas of cortex correspond to areas of the body
