The Nervous system - Introduction to CNS and reflexes (lecture 1) Flashcards
What is the central nervous system comprised of ?
brain and spinal cord
What two types of cells are found in the nervous system ?
neurons and neuroglia
What are the four types of neuroglia cells in the CNS ?
Illustration of the four different types of glial cells found in the central nervous system: ependymal cells (light pink), astrocytes (green), microglial cells (red), and oligodendrocytes (light blue).
What are the two types of neuroglia cells in the peripheral nervous system ?
schwann cells and satillite cells
How many neurones are in the CNS ?
10 to the power of 12 - millions !!
whats makes up the grey matter of a spinal cord cross section ?
dendrites, cell bodies, axon terminals
What happens in the grey matter of the spinal cord ?
Synapses
Whats the white matter composed of ? why white ?
axons - because myelin is white
what are the two types of wings in the spinal cord ?
posterior (dorsal horns) and the anterior (ventral horns)
What are propriospinal neurons?
i have no idea?
What are ascending tracts ?
organised axons that pass information from the spinal cord to higher centres in the brain
What are descending tracts ?
axons that relay commands from the brain and the spinal cord
Where does the term nuclei refer to ?
within the brain, neurones which work together functionally are found in groups known as nuclei.
How do bundles of axons in the brain run ?
longitudinally as well as transversely and thus divides the grey matter into discrete lumps
What does the forebrain, cerebellum and the centrally located grey matter have in common ?
they have a peripheral layer of neurons known as the cortex
What do afferent neurons do ?
sensory fibres relay information to the CNS
What do efferent neurons do ?
motor fibres leave the CNS relaying commands to effectors such as muscle (skeletal, smooth or cardiac )
What do sensory receptors do ?
monitor the external and internal environments for example the visual field or blood pressure
What does the term reflex describe ?
Automatic, reproducible and goal directed responses of an organism to stimuli
What are reflexes involved in ?
homestasis, postural stability others are protective in function
Give me two examples of reflexes ?
cardiovascular reflexes, stretch reflex, the flexor withdrawal reflex
Describe short-loop reflexes refer to ?
reflexes that only require spinal circuitry for example stretch and cutaneous reflexes
Describe long-loop reflexes do ?
reflexes that involve higher centres (i.e. centres in the brain)
How central modulation of reflex arcs occur ?
via descending pathways from higher centres
What does a reflex arc involve ?
sensory receptors, afferent (sensory) neurons, central neurons and efferent (or motor neurons)
What do motor neurons do ?
Excite effectors (skeletal muscle, smooth muscle, cardiac muscle or a gland)
How is the stretch reflex unique ?
it is monosynaptic - i.e one synapse no central neurones involved. The afferents synapse directly onto motoneurons.
What does the stretch reflex act to maintain ?
muscle length and is important in the control of posture
What are the stretch receptors ?
muscle spindles which lie to parallel to the muscle fibres (known as extrafusal fibres)
What are intrafusal fibres ?
muscle fibres contained within the muscle spindle s ?
Tell me a characteristic of intrafusal fibres ?
they are thinner than extrafusal fibres
What do muscle spindles contain ?
intrafusal muscle fibres and stretch receptors
How many types of sensory endings do spindles have
?
two, primary and secondary
What are the primary endings associated with ?
large diameter afferent axons and are sensitive to both the length of the muscle and the rate of the change of length
What are secondary endings sensitive to ?
only muscle length
What do the primary afferents synapse directly with ?
motoneurons of the homonomous (same) muscle (and to a lesser extent onto motoneurons of synergistic muscles) and bring about reflex contraction .
the same afferents also synapse with inhibitory interneurones which inhibit those motoneurons which innervate antagonistic muscles (reciprocal inhibition)
what happens to antagonistic muscles ?
they are relaxed
What can occur during a slow stretch ?
the firing of secondary endings may also contribute to the reflex excitation
what occurs during a withdrawal reflex ? where do the afferent fibres arise from ?
from cutaneous nociceptors
what do the small diameter afferent fibres synapse with during withdrawal reflex ?
The small diameter afferent fibres synapse with a number of interneurons( much divergence) within the dorsal horn of the spinal cord which then synapse with and excite motoneurons of flexor muscles.
Is reciprocal inhibition seen during the withdrawal reflex ?
yes; the afferents synapse with a second group of interneurons which in turn synapse with and inhibit the firing of motoneurons of extensor muscles( i.e muscles which are antagonistic in action to flexor muscles).
What does the excitation of flexor muscles produce ?
A reflex withdrawal of the stimulated limb away from the offending stimulus, so this reflex is protective in function
What are the three protective structures of the CNS ?
Bone, Meninges and cerebrospinal fluid, glial cells, bone, connective tissue
What are meninges ?
the three membranes that line the skull and vertebral canal and enclose the brain and spinal cord.
What are the three meninges ?
(the dura mater, arachnoid, and pia mater)
What is the cranium? function ?
the skull, protects the CNS, i.e protects the brain
What is the vertebrae ?
each of the series of small bones forming the backbone, having several projections for articulation and muscle attachment, and a hole through which the spinal cord passes. the needle is inserted between two of the vertebrae.
What is the cerebrospinal fluid ?
clear, colourless fluid found in the brain and spine. Protects the brain
properties of a unipolar neuron have ? Are they motor neurons ?
one process, one dendrite that splits and one axon.
no they are sensory neurons
properties of a bipolar neuron ? where are they found ?
two processes, one dendrite, and one axon.
In the retina of the eye
properties of pseudo-unipolar cell ? where is it found ?
two processes, one dendrite, and one axon.
Ganglion cell of dorsal root
What are the the three types of multipolar cells ?
normal motor neuron of spinal cord.
Pyramidal cell of hippocampus
purkinje cell of cerebellum
Which matter are the cell bodies and dendrites grouped in ?
gray matter
Which matter are the axons grouped in ?
white matter
What do you call cell bodies in the CNS?
Nuclei
What do you call cell bodies in the PNS ?
Ganglia
What are axons in the CNS referred to as?
pathway projections, tracts , commissures
Axons in the PNS?
Nerves: sensory. motor, mixed
What cell produces myelin in in the CNS ?
oligodendrocytes
give me three examples of involuntary/ automatic motor activity ?
reflexes not under direct control of the brain
postural activity
learnt, skilled activity
Give me two examples of voluntary motor activity ?
Well learnt movements due to practice e.g drinking, driving, sports
Goal directed activity with a degree of conscious attention to the take
Properties of reflexes ?
Simplest motor act
Fast , automatic, stereotyped (reproducible)
involuntary - not under direct control of brain, but often modulated by activity in the CNS
Short loop and long loop ( short/ long latency)
response to specific stimulus
Function of reflexes ?
involved in homeostasis
involved in control of movement
can be protective
after a painful encounter of your toe with a needle what contracts and is inhibited ?
Flexors contract moving painful stimulus away. Extensors on same leg inhibited. on other leg: flexors inhibited.
extensors contract as weight shifts to left leg
What are the components of a reflex arc ?
Receptor: sensor (requires an adequate, specific stimulus)
Afferent neurons: sensory
Interneurons - spinal cord: depends on the type of reflex. monosynaptic = no interneurone
efferent neurons: motor
effector:
muscle: skeletal, cardiac, smooth
Gland
Give me an example of a monosynaptic reflex ?
Stretch reflex
Describe the stretch reflex ?
has both a monosynaptic (no interneurone) and disynaptic component ( 1 interneurone ). This is called reciprocal innervation.
What is the function of the stretch reflex ?
The stretch reflex (myotatic reflex) is a muscle contraction in response to stretching within the muscle. It is a monosynaptic reflex which provides automatic regulation of skeletal muscle length. When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases.
