functional anatomy of the spinal cord

Question 1

what does the cord contain?

Answer 1

-spinal nerves which contain reflex circuits that control rapid reactions to environmental changes
-grey matter
-white matter

Question 2

what is the grey matter of the spinal cord?

Answer 2

-a site for integration of postsynaptic potentials
-it contains the neuron cell bodies and synapses and also has horns

Question 3

what is the white matter of the spinal cord?

Answer 3

-contains major sensory and motor tracts(bundles of axons) that transmit info between the brains and limbs, trunk and organs of the body

Question 4

what are the regions of the spinal cord?

Answer 4

-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

Question 5

what are spinal nerves?

Answer 5

bundles of sensory and motor axons that are paths of communication between the spinal cord and specific regions of the body

Question 6

how are spinal nerves divided?

Answer 6

nerves divide into the anterior (ventral) and posterior (dorsal) roots as they connect to the spinal cord

Question 7

how do ventral and dorsal roots differ?

Answer 7

-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

Question 8

state the different coverings(layers) of the spinal cord?

Answer 8

-spinal meninges
-dura mater
-arachnoid mater
-pia mater

Question 9

what is the spinal meninges?

Answer 9

-tissue coverings that protect the cord and provide physical stability

Question 10

what is the dura mater?

Answer 10

-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

Question 11

what is the arachnoid mater?

Answer 11

-it is attached to the inside of the dura and forms the roof of the subarachnoid space in which cerebral spinal fluid (CSF) circulates

Question 12

what is the Pia mater?

Answer 12

-the pia mater is pressed-up against the cord and is filled with blood vessels that supply nutrients to it

Question 13

how is epidural anaesthesia administered?

Answer 13

-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

Question 14

when and why is anaesthetic given?

Answer 14

-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

Question 15

where is the site used for most lumbar (lower back) punctures?

Answer 15

-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

Question 16

how can CSF be sampled and anaesthetic be given?

Answer 16

-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

Question 17

what type of neurones do the dorsal and ventral horns contain?

Answer 17

dorsal=sensory neurons
ventral=motor neurons

Question 18

state and describe the white matter tracts

Answer 18

-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)

Question 19

how do white matter tracts carry specific kinds of information?

Answer 19

-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

Question 20

what types of sensory information are carried by the dorsal (posterior) column?

Answer 20

-mainly carries touch and proprioception

Question 21

which sensory information is primarily transmitted by the lateral tracts?

Answer 21

the lateral tracts carry mainly pain and temperature senses

Question 22

what is the role of first-order sensory neurons?

Answer 22

-they are PNS and transmit sensory information from the receptor to the spinal cord

Question 23

where are the cell bodies of first-order sensory neurons located?

Answer 23

-the cell bodies of first order sensory neurons are located in the dorsal root ganglion (DRG)

Question 24

how does the axon of a first-order sensory neuron contribute to the transmission of sensory signals?

Answer 24

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

Question 25

where are the cell bodies of second order sensory neurons located?

Answer 25

-in the dorsal horn of the spinal cord

Question 26

what pathway is taken by the axons of secondary-order sensory neurons?

Answer 26

they travel up the spinal cord and decussate (cross) in the brainstem

Question 27

what happens when the icons of second-order neurons decussate in the brainstem?

Answer 27

their axons cross to the opposite side of the brainstem before continuing to the thalamus and synapsing onto third order neurons

Question 28

what is the role of second-order sensory neurons?

Answer 28

they ansmit sensory info from the spinal cord to the thalamus

Question 29

what is the role of third order sensory neurons?

Answer 29

they conduct impulses from the thalamus to the primary somatosensory area of the cortex on the same side

Question 30

what is the function of spinal nerves in relation to dermatomes

Answer 30

-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.

Question 31

how does sensory info from the body reach the brain?

Answer 31

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.

Question 32

what types of sensory modalities are carried by specific tracts in the spinal cord?

Answer 32

-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.

Question 33

how does the brain process sensory input to prevent confusion?

Answer 33

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

Question 34

what is the sensory homunculus and how is it related to the density of sensory input?

Answer 34

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.

Question 35

where does motor activity begin in the nervous system?

Answer 35

in the primary motor areas of the cortex

Question 36

what is an upper motor neuron?

Answer 36

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

Question 37

what is the function of cranial nerves in motor control?

Answer 37

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

Question 38

what is the role of excitatory and inhibitory signals in motor control?

Answer 38

they converge on lower motor neurons to innervate skeletal muscles

Question 39

what is motor neuron disease?

Answer 39

-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

Question 40

what does motor neuron disease cause?

Answer 40

-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

Question 41

what is a reflex arc?

Answer 41

-a pathway that a nerve impulse follows to produce a reflex

Question 42

what are the components of a reflex arc?

Answer 42

-sensory receptor, sensory neuron,an integrating centre inside the cord,an exciting motor neuron and an effector

Question 43

what are effectors?

Answer 43

-muscles or glands that make something move or secrete involuntarily

Question 44

what does transection of the spinal cord mean?

Answer 44

-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

Question 45

what can transection at the base of the skull lead to?

Answer 45

death by asphyxiation

Question 46

what can transection lead to in the upper cervical area and the lower cord enlargement?

Answer 46

-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

Question 47

what is a patellar reflex?

Answer 47

-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)

Question 48

what is the paralysis of the lower motor neurones?

Answer 48

-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.

Question 49

what is the paralysis of the upper motor neurones?

Answer 49

-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.