Brain Flashcards
Central Nervous System (CNS)
Everything inside the spine and skull
cortex, subcortical structures and nuclei, spinal cord
all encased in bone
Peripheral Nervous System (PNS)
everything outside of the spine and skull
Nerves- bundles of axons connecting CNS to body
Ganglion- clusters of cells associated with nerves
PNS system
Has inputs that arrive (Afferent)
Has outputs that exit (Efferent)
Peripheral Motor Output System (Efferent)
Somatic- controls voluntary movement
Autonomic- controls involuntary unconscious movements, has two components
Somatic motor system (efferent)
peripheral nerves exit the spinal cords and contact muscles
stimulation of nerves cause contraction of muscles
controls voluntary movement
Autonomic (efferent)
controls the lungs, heart, smooth muscles and endo and exocrine glands
two autonomic systems work together to to keep system balance
Sympathetic v parasympathetic
Complex system with many functions
Parasympathetic- rest and digest
Sympathetic- fight or flight
Sensory (afferent)
5 basic sensory systems (aware)-
Visual
Auditory
Olfactory (smell)
Gustatory (taste)
Tactile sensation (touch)
Not aware-
Vestibular (sense of head movement in space)
Proprioceptive (sensations from the muscles and joints of the body)
Movements as a circuit
All movements start in the sensory domain from a sensory input
Movements are- in response to an external stimuli (saving penalty)
Directed at an external stimulus (taking penalty)
2 major cell types
Neurones- electrically excitable
cell
communicate
with other cells via
specialized connections
called synapses.
Glial cells-non-neuronal cells in the
nervous system
maintain homeostasis,
form myelin, and
support and protect for
neurones.
Neurone
send and receive signals from your brain.
A cell body, which contains the nucleus and the cytoplasm
An axon, which transmits information away from the nucleus
Dendrites, which receive messages from other neurons.
Information passed through neurones
information passes from the cell body to
the axon terminals via an electrical
signal called an action potential
glia/ glial cells
5 major types of glial cells-
schwann cells
oligodendrocyte
microglial cell
ependymal cells
astrocyte
astrocytes- managing the brain environment
- regulates chemicals around neurones (glucose, ion concentrations, neurotransmitter uptake)
regulate blood flow around the brain
nervous system repair- fill in spaces creating glial scars
maintenance of the blood brain barrier.
Oligodendrocytes
form the myelin sheath on axons
Myelin- a fatty protein rich sheath that wraps around axons
1 can myelinate 50 axons
Schwann cells
form myelin in PNS
assist in regeneration/ regrowth of axons
myelin increases speed
unmyelinated speeds-0.5-10m/s- slow
myelinated speeds-up to 150m/s
creates initial pain/reaction and then secondary worse pain.
microglia
the brains immune system
scavenge the CNS for plaques, damaged cells and infectious agents
ependymal cells
make up the membrane called ependyma
membrane lines central canal of the spinal cord and ventricles
produces cerebrospinal fluid
Summary of cells in the nervous system
CNS-
neurones
microglia
astrocytes
ependymal
oligodendrocytes
PNS-
neurones
satellite
schwann
grey v white matter
myelin is a sheath that insulates many neurones
it is made of fat and proteins and is white
because of this parts of the brain that are many made up of axons are white (white matter).
the brains contains mainly the cell bodies of the neurones - nuclei, ganglion,
cortex - appear pink in the fresh tissue, but grey in perfused
(grey matter).
basic layout of the motor system
- spinal cord
- medulla
- pons
- cerebellum
- midbrain
- thalamus
- basal ganglia
- cerebral cortex
Brainstem``
sits at the top of the spinal cord
made of 3 parts-
medulla
pons
cerebellum``
medulla
the lower half of the brainstem
controls very basic motor functions
cardiac- central chemoreceptors sense oxygen levels- adjust heart rate/ blood pressure
respiration- chemoreceptors sense change in blood chemistry- increase breathing rate
reflexes- vomiting’s, coughing, sneezing and swallowing
`pons
contains nuclei that relay signals from forebrain to the cerebellum
nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation and posture
cerebellum
maintenance of balance and posture
coordination of movements- especially across joints
motor learning
midbrain
tectum controls rapid orientation of the head and neck-
superior colliculus- vision
inferior colliculus- sound
substantia nigra- Parkinson’s disease
associated with sleep, wake cycles, alertness, temp regulation
thalamus
acts as a switchboard
takes information from PNS and passes to cortex
NB- hypothalamus
hormones
metabolic control e.g. hunger, body temp
cerebral cortex
it plays a key role in:
* movement
* attention
* perception
* awareness
* thought
* memory
* language
* consciousness
basal ganglia
- a series of
interconnected nuclei - movement regulation
- skill learning
- habit formation
- reward systems
- selection of appropriate
behaviours - self-initiation of
behaviours
Spinal cord
Pathways to and from the brain
Cell and white matter
in the spinal cord
the middle of the cord (that looks a bit
like an H) is made up of neurones and
other cells (grey matter).
outside cord- made up of fibres (white matter) carry information up and down the cord.
sensory information
touch
proprioception
vibration
pain
temperature
sensory information enters the spinal cord at the dorsal horn
Motor neurones
located in the ventral spinal cord
the neurones make direct contact onto muscles
stimulation causes movement
each cell is part of a motor unit
Muscles are controlled by a “motor pool” of Neurones
all motor neurones that innervate a single muscle are called a motor pool
more muscle fibres than neurones
so each fibre is innervated by a single neurone
but one neurone may innervate many fibres
The size of this innervation is important as muscles that are capable of fine movements are innervated by more neurones.
somatotopy
Maps are referred to as
‘somatotopic’ when that
space is related to
locations on the body, such
that adjacent neurons in
the neural tissue respond
selectively to stimuli
presented to adjacent
locations on the body.
Spinal White Matter
fibre tracts that carry information to and from the brain
Lateral descending
system
The corticospinal and rubrospinal
tracts
Medial descending
system
The vestibulospinal and reticulospinal
tracts
Lateral descending system
The corticospinal and rubrospinal tracts make up the the lateral descending system
- fibres of the lateral system are in the dorso-
lateral part of the spinal cord. - they connect to motor neurones in the
lateral part of the ventral horn. - this system influences lateral musculature.
lateral system – round up
Corticospinal fibers strongly influence movement of every part of the body and is particularly useful for individual finger use.
- Other descending fibers, primarily the rubrospinal tract, can compensate
almost completely for the loss of descending corticospinal input. - The one ability of the descending corticospinal tract for which no other
tract can compensate is the ability to use the fingers individually.
Individual finger movements are the sole province of the corticospinal
system.
Medial system (vestibulospinal and reticulospinal tracts)
The vestibulospinal and reticulospinal
tracts make up the the medial descending
system.
- fibres of the medial system are in the
ventro-medial part white matter. - they connect to motor neurones in the
medial part of the ventral horn. - this system influences medial musculature.
medial systems – round up
- the medial systems are involved in the control of balance and
posture. - these functions happen with little conscious control.
- the vestibulospinal tract retains balance when the body is
moved – external disturbance. - the reticulospinal tract helps us retain posture and balance
during our own volitional movements – internal disturbance.
dorsal column pathway
carries sensory information
from the joint and skin about:
* fine touch.
* vibration.
* two-point discrimination.
* proprioception (position) from
the skin and joints.
Spinothalamic pathway
The lateral spinothalamic tract
conveys
* crude touch.
* a sense of being touched
without knowledge of where.
* pain.
* temperature.
Nerves
Regardless of where
the cell bodies are,
both the sensory and
motor axons run in
the same nerves.
* These nerves are
spinal nerves.
Information in and out of the spinal cord
The cell bodies of incoming sensory neurones lie outside the spine in a
series of ganglion – called the Dorsal Root Ganglion (DRG)
This is unlike the motor neurones that have their cell bodies in the
ventral horn.
spinal nerves
- There are 31 pairs of spinal nerves.
- The positions in the spine these
nerves will determine what part of
the body each spinal nerve serves. - Because some parts of the body
have more muscles and more
sensory receptors. The size of the
nerve and the amount of
information carried by the nerve will
be different.
Dermatomes
an area of the skin
supplied by nerves
from a single spinal
root
Shingles
Chickenpox is caused by
the varicella zoster virus ).
After recovery the virus
remains in your DRG.
* Sometimes in later life the
virus can reactivate
producing a painful or
itchy rash that is isolated
to a single dermatome
2 – point
discrimination
is the ability to
discern that two
nearby objects
touching the
this ability reflects
how finely innervated
an area of skin is
Motor pools are made of motor units
Motor units make up motor pools:
* a lower motor neurone (or alpha
motor neurone) in the spinal
cord innervates a muscle.
* each motor neuron synapses
with multiple fibres within the
muscle. The motor neurone
and all the muscle fibres it
contacts define the motor unit.
* cross section through the muscle
shows the relatively diffuse
distribution of muscle fibres (dark
fibres) contacted by a single
motor neuron
Spinal Enlargements
he arms and legs (particularly the
hands and feet) have many highly
innervated muscles and have a
high density of sensory receptors.
Because of this the portions od
the spinal cord that provide the
spinal nerves to the arms and
legs are enlarged
information flow in a spinal segment
- dorsal horn - contains sensory
neurones. these receive
sensory information and send
this up to the brain. - Ventral horn – contain
neurones that send messages
directly to the muscles. - intermediate zone –contain
interneurones. these integrate
information. e.g – inhibition.
coding in nervous systems is by action potentials
timulus
intensity
determines size
of receptor
potential & thus
frequency of
action
potentials
firing frequency codes for
intensity (“rate code”)
very non-linear
usually codes for intensity
of contrast between two
levels.
rate coding in the motor system
- Motor neurons use a rate
code to signal the
amount of force to be
exerted by a muscle. - An increase in the rate
of action potentials fired
by the motor neuron
causes an increase in
the amount of force that
the motor unit generates.
rate coding in the motor system
- recruitment & size principle
- For small forces small
motor units are
recruited first, as the
required force
increases, larger motor
units are recruited. - Size principle states
that, with increasing
strength of input onto
motor neurons,
smaller motor neurons
are recruited and fire
action potentials
before larger motor
neurons are recruited.
early effects of training
are neuronal in origin
- humans before and after
dynamic training. - Note
the increased rate of
tension development after
dynamic training - increased rate of of tension
achieved after training is
accompanied increase in
rectified surface EMG
activity in the early phase
of contraction.
Subcortial control of movement
Title
spinal cord reflexes
e.g. stretch reflex
Stretching a muscle is detected in the muscle and
leads to increased activity in sensory neurones that in
turn leads to an increase in the activity of motor
neurons that innervate the same muscle, while
inhibiting the motor neurons that innervate
antagonists.
Reflexes
- rapid automatic control of movement.
- little or no voluntary control.
- some are very simple:
- stretch reflex.
- some are more complex:
- swallowing, breathing.
- these mainly happen in the spinal cord and low in the brain
stem.
brainstem
the brainstem sits at the top
of the spinal cord and is
made of three parts:
1. medulla
2. pons
3. midbrain
2 important brainstem nuclei groups
The reticular formation is a set of
interconnected nuclei that are
located throughout the brainstem.
The vestibular nuclei (VN) are the
nuclei for the vestibular system
and are located in the brainstem.
Vestibulospinal tract
The vestibular system is thesensory system that provides the
sense of balance and spatial orientation for the purpose of coordinating movement with
balance
The vestibulospinal tract originates in the vestibular nuclei. They send
most of their output to the spinal cord and to the muscles that move
the eyes.
Reticulospinal
Tract
- the reticular formation is a set of interconnected nuclei that are located throughout the brainstem.
- It is a very old part of the brain.
- The reticulospinal tract originates in reticular formation.
- These tracts function in maintaining tone, balance, and posture.
cerebellum
- the cerebellum has a very
conserved, highly folded
structure in all animals - 10% volume of the brain.
- More than neurones than
the cortex. - 69Billion v 16Billion
- input:output connections
ratio. - 40:1
input/output (40:1)
Superior cerebellar peduncle
* efferent (out) pathway to the red
nucleus and the cortex (via the
thalamus) & sup colliculus.
Middle cerebellar peduncle:
* most fibres originate in the pons
* input from sensory, visual, vestibular
and motor systems.
* but its largest input is from the cortex.
Inferior cerebellar peduncle
* carries information to and from the the
spinal cord (and the body) and
vestibular nuclei
Rubrospinal Tract
The red nucleus is a roughly spherical
collection of cell bodies in the midbrain.
It is called the red nucleus because it is
extremely vascular. In fresh tissue the
red nucleus is distinctly pinker than the
surrounding tissue.
The red nucleus receives a very large
input from the cerebellum and from the
primary motor cortex.
basal ganglia
- movement regulation
- skill learning
- habit formation
- reward systems
- selection of appropriate
behaviours - self-initiation of
behaviours
2 pathways- through the basal ganglia
- the DIRECT pathway
that runs DIRECTLY
through the basal
ganglia - the INDIRECT
pathway takes a
longer loop through
the basal ganglia.
the loops start and finish in the cortex
DIRECT
* short loop though the basal
ganglia.
* has excitatory effect on
cortex.
* Net effect is pro-movement.
INDIRECT
* long loop through the basal ganglia.
* has inhibitory effect on
cortex.
* Net effect is anti-movement.
the BG and cerebellum do
different/complementary things
basal ganglia
* damage to the BG produces
states where there is too
much, or too little movement.
cerebellum
* damage to the cerebellum
produces states where
movements can still be made,
but they are uncoordinated.
cortical control of movement
title
Brain maps - homunculi
- Because of the close
relationship with the body
surface & muscles, both the
primary sensory and motor
cortex have detailed
somatotopic maps of the body in
them. - Areas of the body with many
highly innervated muscles and
densely packed sensory
receptors have expanded
representations in the brain.
- primary motor cortex
Neurones in the primary motor cortex
have a simple relationship to movement.
They fire around 5 to 100 ms before
movement onset and can code for the
basic parameters of movement, i.e.:
* Force.
* Direction.
* Extent.
* Speed
- other motor cortical
regions exist (area 6)
As we have seen neurones in the
primary motor cortex have a simple
relationship with movement
parameters.
Neurones in the non-primary motor
cortex have a more complex
relationship to movement. They code
for the more complex aspects of
movement
pre-motor cortex (orange
area 6)
Neurones in the non-primary motor cortex
have a more complex relationship to
movement. They code for the more complex
aspects of movement, for example:
* planning movement.
* spatial guidance of movement.
* sensory guidance of
movement.
Supplementary motor cortex
(SMA; purple area 6)
Neurones in the non-primary motor cortex
code for more complex aspects of
movement. They code for the more
complex aspects of movement, for
example:
* coordinating temporal sequences of
actions.
* bimanual coordination.
* initiation of internally generated as
opposed to stimulus driven
movement *NB – the SMA is well
connected to the basal ganglia.
SMA – bimanual coordination
- A monkey is trained to
perform a complex
bimanual task that
requires the animal to
push a peanut through a
hole to collect a peanut. - After a lesion of the SMA
the animal cannot perform
this task and the function
does not recover
Areas closely associated with movement
These area are needed for complex movements and are highly interconnected with the motor areas
primary sensory
cortex (areas 1, 2 &
3)
- touch: vibration, heat, pain, pressure.
- Proprioception: Afferent information, including
joint position sense, kinesthesia, and sensation
of resistance: - Joint position sense: The ability to
recognize joint position in space. - Kinesthesia: The ability to appreciate and
recognize joint movement or motion. - Sensation of resistance: The ability to
appreciate and recognize force generated
within a joint.
posterior parietal
cortex. (areas 5&7)
- integration of sensory, visual
information to execute complex
movement in the environment. - representations for different motor
effectors (e.g. arm vs. eye) - a command apparatus for operation
of the limbs, hands and eyes within
immediate extrapersonal space
corticospinal tract
The most important tract in the
human for precise control of the
limbs.
* Origin:
* primary motor cortex (30%)
* Premotor, supplementary (30%)
* Somatosensory, parietal,
cingulate (40%)
* About 1 million fibers in humans.
* 90% cross at lower medulla
* All are excitatory
Increasing complexity as we go ‘up’ in the brain
he complexity of the movements the
nervous system controls increases as you
move toward (and through the brain):
spinal cord – simple reflexes.
medulla – complex reflexes.
cerebellum – coordinated movement.
basal ganglia – programmed movements.
cortex – complex conscious movements.
