functional anatomy of the spinal cord Flashcards
-Basic concepts of the functional anatomy of the spinal cord -Internal anatomy of the spinal cord -The sensory system -The motor system
what does the cord contain?
-spinal nerves which contain reflex circuits that control rapid reactions to environmental changes
-grey matter
-white matter
what is the grey matter of the spinal cord?
-a site for integration of postsynaptic potentials
-it contains the neuron cell bodies and synapses and also has horns
what is the white matter of the spinal cord?
-contains major sensory and motor tracts(bundles of axons) that transmit info between the brains and limbs, trunk and organs of the body
what are the regions of the spinal cord?
-the spinal cord begins as a. continuation of the medulla oblongata to the conus medullaris
-it has a cauda equine (horses tail)=roots of the lower spinal nerves
-it has cervical,thoracic,lumbar and sacral regions
-has plexuses where the nerves join together
what are spinal nerves?
bundles of sensory and motor axons that are paths of communication between the spinal cord and specific regions of the body
how are spinal nerves divided?
nerves divide into the anterior (ventral) and posterior (dorsal) roots as they connect to the spinal cord
how do ventral and dorsal roots differ?
-ventral roots contain axons of motor neurones which conduct nerve impulses from the CNS to effectors (muscles and glands)
-dorsal roots contain sensory axons, which have terminals at sensory receptors with cell bodies in the dorsal root ganglion and axons synapse in the spinal cord
state the different coverings(layers) of the spinal cord?
-spinal meninges
-dura mater
-arachnoid mater
-pia mater
what is the spinal meninges?
-tissue coverings that protect the cord and provide physical stability
what is the dura mater?
-the thought mother which forms a sac that encloses the entire spinal cord, there is epidural space that lies between the dura and the inner surface of the bony vertebrae
what is the arachnoid mater?
-it is attached to the inside of the dura and forms the roof of the subarachnoid space in which cerebral spinal fluid (CSF) circulates
what is the Pia mater?
-the pia mater is pressed-up against the cord and is filled with blood vessels that supply nutrients to it
how is epidural anaesthesia administered?
-a needle is placed between the bones of the posterior spine until it just penetrates the ligaments flavour yet remains superficial to the dura mater
when and why is anaesthetic given?
-epidural anaesthesia is given to women who atrophy about to go on labour
-local anaesthetic is given to provide pain relief whilst complete anaesthesia can also be given if a caesarean section is needed
where is the site used for most lumbar (lower back) punctures?
-between the 3rd and 4th (or 4th and 5th) and the lumbar vertebrae-below the termination of the actual cord in the region of the cauda equina
how can CSF be sampled and anaesthetic be given?
-with a needle in the subarachnoid space,CSF can be sampled and anaesthetic can also be given but only using 1/10th of the dose required for epidural anaesthesia
what type of neurones do the dorsal and ventral horns contain?
dorsal=sensory neurons
ventral=motor neurons
state and describe the white matter tracts
-the spinothalamic tract-it transmits sensory info from the spinal cord to the brain (ascending)
-the corticospinal tract-it transmits motor info from the brain to the spinal cord (descending)
how do white matter tracts carry specific kinds of information?
-the different motor tracts carry nerve impulses from specific areas of the brain to the body e.g
-the lateral corticospinal tract controls precise, agile,highky skilled movements of the hands and feet
-the ventricular (anterior) corticospinal tract controls movement pf the trunk and limbs
what types of sensory information are carried by the dorsal (posterior) column?
-mainly carries touch and proprioception
which sensory information is primarily transmitted by the lateral tracts?
the lateral tracts carry mainly pain and temperature senses
what is the role of first-order sensory neurons?
-they are PNS and transmit sensory information from the receptor to the spinal cord
where are the cell bodies of first-order sensory neurons located?
-the cell bodies of first order sensory neurons are located in the dorsal root ganglion (DRG)
how does the axon of a first-order sensory neuron contribute to the transmission of sensory signals?
the axon of the first order neuron carries the sensory signal from the receptor to the spinal cord where it synapses onto a second-order neuron
where are the cell bodies of second order sensory neurons located?
-in the dorsal horn of the spinal cord
what pathway is taken by the axons of secondary-order sensory neurons?
they travel up the spinal cord and decussate (cross) in the brainstem
what happens when the icons of second-order neurons decussate in the brainstem?
their axons cross to the opposite side of the brainstem before continuing to the thalamus and synapsing onto third order neurons
what is the role of second-order sensory neurons?
they ansmit sensory info from the spinal cord to the thalamus
what is the role of third order sensory neurons?
they conduct impulses from the thalamus to the primary somatosensory area of the cortex on the same side
what is the function of spinal nerves in relation to dermatomes
-Spinal nerves innervate specific areas of the skin called dermatomes, which are areas of the skin supplied by a particular spinal nerve.
-These dermatomes are labeled with letters and numbers based on the spinal nerve.
how does sensory info from the body reach the brain?
Sensory information from specific areas of the body is transmitted through the spinal nerves to the spinal cord and then to the cortex for processing.
what types of sensory modalities are carried by specific tracts in the spinal cord?
-Different sensory modalities are carried in distinct tracts in the spinal cord.
For example:
Touch is carried in the dorsal column.
Pain is carried in the lateral tracts.
how does the brain process sensory input to prevent confusion?
The brain processes sensory input from specific parts of the body in distinct cortical areas and layers, which prevents sensory information from being mixed up and kept distinct
what is the sensory homunculus and how is it related to the density of sensory input?
The sensory homunculus is a representation of the body in the brain, where peripheral areas with the highest density of sensory receptors (like the lips and thumbs) are represented by a larger amount of gray matter.
where does motor activity begin in the nervous system?
in the primary motor areas of the cortex
what is an upper motor neuron?
An upper motor neuron is a motor neuron that does not directly stimulate target muscles they also connect the brain to the appropriate level in the spinal cord
what is the function of cranial nerves in motor control?
they carry the axons of lower motor neurons to innervate the skeletal muscles of the face and head and through spinal nerves to innervate skeletal muscles of the limbs and trunk
what is the role of excitatory and inhibitory signals in motor control?
they converge on lower motor neurons to innervate skeletal muscles
what is motor neuron disease?
-A progressive degenerative disease that attacks motor areas of the cerebral cortex,axons of the upper motor neuroms and lower motor neuron cell bodies
-It begins in sections of the spinal cord that serve the hands and arms but rapidly spread to involve the whole body and face
what does motor neuron disease cause?
-progressive weakness and atrophy (the partial or complete wasting away)
-death occurs typically in 2-5yrs
-Inherited mutations account for 15% of cases,non inherited cases have several implicating factors e.g glutamate build up (excitotoxicity) due to defective uptake
-the drug riluzole reduces damage by decreasing the excitotoxic effects of glutamate
what is a reflex arc?
-a pathway that a nerve impulse follows to produce a reflex
what are the components of a reflex arc?
-sensory receptor, sensory neuron,an integrating centre inside the cord,an exciting motor neuron and an effector
what are effectors?
-muscles or glands that make something move or secrete involuntarily
what does transection of the spinal cord mean?
-the ascending and descending tracts are partially or completely severed
-if transection occurs e.g due to a motor vehicle accident paralysis will occur depending on the level of injury
what can transection at the base of the skull lead to?
death by asphyxiation
what can transection lead to in the upper cervical area and the lower cord enlargement?
-for the upper cervical are -quadriplegia in all 4 limbs
-in the lower cord enlargements-some form of paraplegia (the inability to move the lower parts of the body
what is a patellar reflex?
-where a branch of the sensory neuron directly stimulates the spinal motor neuron which cause a reflex kick at the same time as sending info to the brain
-fractions of a second later, the sensory info reaches the brain, sending a motor signal down the spinal cord to control the muscle contraction (this is how movements are controlled)
what is the paralysis of the lower motor neurones?
-damage or disease of lower motor neurons produces flaccid paralysis.
- There is neither voluntary or reflex action of the innervated motor fibres, muscle tone is decreased or lost, and the muscle remains limp or flaccid.
what is the paralysis of the upper motor neurones?
-injury or disease in the cerebral cortex removes inhibitory influences on lower motor neurones, causes spastic paralysis of muscles on opposite side of the body. Muscle tone is increased, reflexes are exaggerated.
