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Human Physiology > Week 3: Human Brain > Flashcards

Week 3: Human Brain Flashcards

1
Q

what are the functions of the brain

A
  • interpreting all information from the outside world
  • the seat of the higher functions:
    • the mind
    • intelligence
    • creativity
    • emotion
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2
Q

are larger brains better

A

bigger, more complex brains allow for more complex motor behaviours

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3
Q

what part of the brain make up the motor system

A
  • spinal cord
  • medulla
  • pons
  • cerebellum
  • midbrain
  • thalamus
  • basal ganglia
  • cerebral cortex
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4
Q

where is the brainstem and what is it made up of

A
  • it sits at the top of the spinal cord and is made up of three parts
    • medulla
    • pons
    • cerebellum
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5
Q

what is the medulla

A
  • the lower half of the brain stem - right on top of the spinal cord. controls basic motor functions
    • cardiac: central chemoreceptors sense oxygen levels in the brain and alter heart rate and blood pressure
    • respiration: chemoreceptors sense changes in blood and increase breathing rate
    • reflexes: vomiting, coughing, sneezing and swallowing
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6
Q

what are the pons

A
  • contains nuclei that relay signals from the forebrain to the cerebellum
  • nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensations and posture
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7
Q

what is the cerebellum

A
  • maintenance of balance and posture
  • coordination of movements (especially across multiple joints)
  • motor learning
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8
Q

what is the midbrain

A
  • tectum controls rapid orientation of the head and neck
    • superior colliculus (vision)
    • inferior colliculus (sound)
  • substantia nigra
    • Parkinson’s disease
  • also associated with sleep and wake cycles, alertness and temperature regulation
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9
Q

what is the thalamus

A
  • bottom of forebrain (diencephalon)
  • acts as a switchboard
  • takes information from the periphery and passes it to the cortex
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10
Q

what is the hypothalamus

A
  • bottom of forebrain (diencephalon)
  • hormones
  • metabolic control
    • hunger
    • body temperature
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11
Q

what is the basal ganglia

A
  • a series of interconnected nuclei
  • movement regulation
  • skill learning
  • habit formation
  • reward systems
  • selection of appropriate behaviors
  • self initiation of behaviors
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12
Q

what is the cerebral cortex

A
  • it plays a key role in:
    • movement
    • attention
    • perception
    • awareness
    • thought
    • memory
    • language
    • consciousness
  • cortical sheet has 6 layers
  • there are folds (gyri) and grooves (sulci)
  • 2-4mm thick
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13
Q

what are the four lobes of the brain

A
  • frontal lobe
  • parietal lobe
  • occipital lobe
  • temporal lobe
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14
Q

what is the frontal lobe

A
  • frontal association area
  • speech
  • motor cortex
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15
Q

what is the parietal lobe

A
  • somatosensory cortex
  • speech
  • taste
  • somatosensory association area
  • reading
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16
Q

what is the occipital lobe

A
  • visual association area
  • vision
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17
Q

what is the temporal lobe

A
  • auditory association area
  • hearing
  • smell
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18
Q

what is the calculation for brain size

A

brain = (3/4 of body) / 21

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19
Q

how are primate brains different

A
  • in most animals, as brains get bigger, so do the neurons
  • this isn’t the case with primates where the neurons remain the same size
  • this means we can pack in more neurons
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20
Q

how many neurons are there in total, cerebral cortex, cerebellum and basal ganglia/thalamus/brainstem

A

total = 86 billion
cerebral cortex = 16 billion
cerebellum = 69 billion
basal ganglia / thalamus / brainstem = 0.7 billion

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21
Q

what does isotropic mean

A

having a physical property which has the same value when measured in different directions

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22
Q

what is the method for counting cells

A
  • by dissolving the cells and surrounding structure but leaving each cell nuclei whole
  • these nuclei are a isotropic suspension
  • you can stain all the cells for DNA (blue) and the neurons (red)
  • then you just subtract one from the other in a known volume of suspension and factor up
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23
Q

what is the energy consumption of the brain like

A
  • the human brain consumes 20% of the total energy generate in the body - although it represents only 2% of the total body weight
  • 15-20% of the total cardiac output is directed to the brain
  • energy restrictions mean that you can have a big brain or a big body but not both
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24
Q

what movements do the cerebrum, tectum, cerebellum and spinal cord/hindbrain create

A
  • cerebrum
    • volitional movements
  • tectum
    • contains areas that control movements in response to external stimuli
  • cerebellum
    • coordination
  • spinal cord/hindbrain
    • automatic movements, coordination, breathing, posture, balance, gait
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25
Q

what are spinal reflexes

A
  • simple reflexes are stereotyped movements elicited by the activation of skin or muscle receptors and are the basic unit of movements
  • complex sequences of movements can be produced by combining simple reflexes
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26
Q

what is the stretch reflex

A
  • monosynaptic and synaptic components
  • large diameter sensory fibers (1a afferents, fast) are coiled around muscle spindles
  • stretch imposed on a muscle is detected by muscle spindles
  • this initiates action potentials in these specialised sensory nerves toward the spinal cord
  • these synapse with motor neurons that innervate the same muscle causing contraction
  • 1a sensory neurons activate local inhibitory connections for the antagonistic muscles
  • the net results work against the applied force - and fast
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27
Q

what is the withdrawal reflex

A
  • the quick contraction of flexor muscles resulting in the withdrawal of a limb
  • required coordinated movements of limbs
  • polysynaptic reflex arc - though relatively complex, the behavior is still produced at the level of the spinal cord
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28
Q

what is a sensorimotor

A
  • most movements are in response to outside stimulus
  • the simplest movements are reflexes and these are:
    • quick
    • stereotyped
    • very very rapid
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29
Q

why is the cells and white matter in the spinal cord

A
  • the middle of the cord is made up of neurons and other cells (grey matter)
  • the outside of the cord is made up of the fibres (white matter) that carry information up and down the cord
  • these sections are stained for the myelin that covers the fibres, so that the white matter stained dark
  • 4 sections: cervical, thoracic, lumbar, sacral
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30
Q

what is sensory information (Dorsal horn)

A
  • fine touch
  • proprioception
  • vibration
  • pain
  • temperature
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31
Q

what are motor neurons (ventral horn)

A
  • make direct contact onto the muscles
  • stimulation of these neurons causes movement
  • each cell is part of a motor unit
32
Q

what is somatotopy

A

maps are referred to a ‘somatotopic’ when that space is relaxed to locations on the body, such that adjacent neurons in the neural tissue respond selectively to stimuli presented to adjacent locations on the body

33
Q

what is the lateral descending system

A
  • the corticospinal and rubrospinal tracts
  • fibres of the lateral system are in the dorso-lateral part of the spinal cord
  • they connect to motor neurons in the lateral part of the ventral horn
  • this system influences lateral musculature
  • corticospinal fibres strongly influence movement of every part of the body and is particularly useful for individual finger use
  • other descending fibres 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
34
Q

what is the medial descending system

A
  • the vestibulospinal system and reticulospinal system
  • fibres of the medial system are in the ventro-medial part of white matter
  • they connect to motor neurons in the medial part of the ventral horn
  • this system influences medial musculature
  • 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
35
Q

what is the medial lemniscus / dorsal column pathway

A
  • carries sensory information from the joint and skin about:
    • fine touch
    • vibration
    • two-point discrimination
    • proprioception (position) from the skin and joints
36
Q

what is the spinothalamic tract

A
  • the lateral spinothalamic tract conveys:
    • crude touch
      • sense of being touched without knowledge of where
    • pain
    • temperature
37
Q

where do you find sensory and motor neurons

A
  • the cell bodies of incoming sensory neurons lie outside the spine in a series of ganglion - called the dorsal root ganglion (DRG)
  • this is unlike the motor neurons that have their cell bodies in the ventral horn
  • regardless of where the cell bodies are, both the sensory and motor neurons run in the same nerves
  • these nerves are spinal nerves
38
Q

what is the function of spinal nerves

A
  • 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
39
Q

what are dermatomes

A

an area of the skin supplied by nerves from a single spinal root

40
Q

what are shingles

A
  • 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
40
Q

what are shingles

A
  • 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
41
Q

what is two point discrimination

A
  • is the ability to discern that two nearby objects touching the skin
  • the ability reflects how finely innervated an area of skin is
42
Q

what is a motor pool

A
  • all the motor neurons that innervate a single muscle are called a motor pool
  • because there are more muscle fibres than neurons, each muscle fibre is innervated by a single neuron, but a single motor neuron may innervate many fibres in the same muscle
  • the size of this innervation is important as muscles that are capable of fine movements are innervated by more neurons
43
Q

how do motor units make up motor pools

A
  • a lower motor neuron (or alpha motor neuron) in the spinal cord innervates a muscle
  • each motor neuron synapses with multiple fibres within the muscle. the motor neuron and all the muscle fibres contracting defines the motor unit
  • cross section through the muscle shows the relatively diffuse distribution of muscle fibres (dark fibres) contacted by a single motor neuron
44
Q

what is spinal enlargement

A
  • the 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 of the spinal cord that provide to the arms and legs are enlarged
45
Q

how does information flow in the spinal cord

A
  • dorsal horn: contains sensory neurons. these receive sensory information and send this up to the brain
  • ventral horn: contains neurons that send messages directly to the muscles
  • intermediate zone: contain interneurons - these integrate information e.g. inhibition
46
Q

how does coding occur in the sensory system

A
  • stimulus intensity determines size of receptor and thus frequency of action potentials
  • firing frequency codes for intensity (“rate codes”) very non-linear usually codes for intensity of contrast between two levels
47
Q

what is rate coding in the motor system

A
  • 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 neurons causes an increase in the amount of force that the motor unit generates
  • single action potentials will produce single twitches
  • when multiple potentials occur in quick succession the force in the muscle builds up
  • at a certain rate the muscle will be unable to contract further - maximal contraction
  • this maximal contraction is called a tetanic contraction and occurs when the input is at a frequency that is so fast that the muscle cannot relax between action potentials
48
Q

what is recruitment and size principle

A
  • 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
49
Q

why are the early effects of training neuronal in origin

A
  • humans before and after dynamic training - note the increased rate of tension development after dynamic training
  • increased rate of tension achieved after training is accompanied with an increase in rectified surface EMG activity in the early phase of contraction
50
Q

what is the basic layout of the subcortical motor system

A
  • spinal cord
  • medulla
  • pons
  • cerebellum
  • midbrain
  • thalamus
  • basal ganglia
51
Q

what is the stretch reflex

A

stretching a muscle is detected in the muscle and leads to increased activity in sensory neurons 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

52
Q

what reflexes create simple movements

A
  • 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 brainstem
53
Q

where is the brainstem

A
  • the brainstem sits at the top of the spinal cord and is made up of three parts:
    • medulla
    • pons
    • midbrain
54
Q

what are the two different brainstem nuclei groups

A
  • the reticular information 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
55
Q

what is the vestibulospinal tract

A
  • the vestibular system is the sensory 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
56
Q

what is the function of the vestibulospinal tract

A

helps out body to alter posture and position to help feel safer

57
Q

what is the reticulospinal tract

A
  • 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
58
Q

what is the cerebellum

A
  • the cerebellum has a very conserved, highly folded structure in all animals
  • 10% volume of the brain
  • more neurons than the cortex
    • 69B vs 16B
  • input : output connections ratio
    • 40:1
59
Q

what are the roles of different sections of the cerebellum

A
  • superior cerebellar peduncle
    • efferent (out) pathway to the red nucleus and the cortex (via the thalamus) and supcalliculus
  • 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 spinal cord (and the body) and vestibular nuclei
60
Q

what is the rubrospinal tract

A
  • 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
  • rubrospinal fibres that originate in the red nucleus cross the midline immediately after exiting the nucleus. They then course in the ventrolateral part of the brainstem to the cord. In the cord rubrospinal fibres occupy the same part of the white matter as the corticospinal tract
  • rubrospinal fibres terminate primarily in the cervical and lumbar enlargements of the cord, which contain motor neurons for muscles in the fore and hind limbs respectively
  • recording data indicate that the rubrospinal tract controls the shaping of the hand during reach-to-grasp movements
61
Q

what is the function of the basal ganglia

A
  • movement regulation
  • skill learning
  • self initiation of behaviors
  • habit formation
  • reward systems
  • selection of appropriate behaviors
62
Q

what are the two different pathways through the basal ganglia

A
  • there are two pathways through the basal ganglia
    • the direct pathway 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 through basal ganglia
      • has exitatory effect on cortex
      • net effect is pro-movement
    • indirect
      • long loop through basal ganglia
      • has inhibitory effect on cortex
      • net effect is any-movement
63
Q

basal ganglia vs cerebellum

A
  • damage to the basal ganglia produces states where there is too much or too little movement
  • damage to the cerebellum produces states where movements can be made but they are uncoordinated
64
Q

what are brain maps (homunculi)

A
  • because of the close relationship with the body surface and muscles, both the primary sensory and motor cortex have detailed somatotopic maps of the body in them
  • areas of the body with highly innervated muscles and densely packed sensory receptors have expanded representations in the brain
65
Q

what is the motor area in the cortex

A
  • the three main cortical motor systems can be identified because:
    • neurons increase their firing rates before movements and specific features of this activity are often closely related to specific movement features
    • neurons send their axons to terminate in motor centre in the brainstem and spinal cord
    • electrical stimulation in these areas elicits movements
    • neurons send their axons to connect most densely with other motor areas
66
Q

what is the primary motor cortex

A
  • neurons in the primary motor cortex have a simple relationship to movement. they fire around 5-100ms before movement onset and can code for the basic parameters of movement i.e:
    • force
    • direction
    • extent
    • speed
67
Q

what are the other motor cortical regions

A
  • as we have seen, neurons in the primary motor cortex have a simple relationship with movement parameters
  • neurons in the non-primary motor cortex have a more complex relationship to movement. they code for the more complex aspects of movement
68
Q

what is the pre motor cortex

A
  • neurons in the pre motor cortex code for more complex parameters of movement i.e:
    • planning movement
    • spatial guidance of movement
    • sensory guidance of movement
69
Q

what is the supplementary motor cortex

A
  • neurons in the supplementary motor cortex code other complex aspects of movement that are different to those in the pre motor cortex i.e:
    • coordinating temporal sequences of actions
    • bimanual coordination
    • initiation of internally generated as opposed to stimulus driven movement
70
Q

what is SMA - bimanual coordination

A

loss of ability to coordinate both limbs if working at same time is SMA is damage

71
Q

what is the primary sensory cortex

A
  • touch: vibration, heat, pain, pressure
  • proprioception: afferent information including joint position sense, kinesthesia, and sensation of resistance
    • joint position sense: the ability to recognise joint position in space
    • kinesthesia: the ability to appreciate and recognise joint movement or motion
    • sensation of resistance: the ability to appreciate and recognise force generated within a joint
72
Q

what is the posterior parietal cortex

A
  • integration of sensory, visual information to execute complex movement in the environment
  • representations for different motor effectors (e.g. arms vs eye)
  • a command apparatus for operation of the limbs, hands and eyes within immediate extrapersonal space
73
Q

what is the corticospinal tract

A
  • the most important tract in the human body for precise control of the limbs
  • origin:
    • primary motor cortex (30%)
    • premotor, supplementary (30%)
    • somatosensory, parietal, angulate (40%)
  • about 1 million fibres in humans
  • 90% cross at lower medulla
  • all are excitatory
74
Q

which areas of the brain are more complex

A
  • the complexity of the movements the nervous system controls increases as you move towards (and through) the brain:
    • spinal cord: simple reflexes
    • medulla: complex reflexes
    • cerebellum: coordinated movement
    • basal ganglia: programmed movements
    • cortex: complex conscious movements

Human Physiology (11 decks)

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