What are afferent fibers?

Afferent fibers are sensory fibers which convey information towards the CNS

What are efferent fibers?

Efferent fibers are motor fibers which convey information from the CNS

How are the terms afferent and efferent used?

They are used to describe projections to and away from neurons (respectively)

What does "rostral" mean?

It means "towards the tip of the head"

What does "caudal" mean?

It means "towards the tip of the tail"

What does "dorsal" mean?

It means "upper surface of the body"

How does the human brain/spinal chord combination differ from that of other animals (ex: a fish)?

The flat plain of the human brain forms a 90^o angle with the direction of the spinal chord unlike other 4-legged animals where this same plain exists at a flat (0^o) angle. In humans, "anterior" replaces the term "rostral" and "posterior" replaces the term "caudal"

What does "ventral" mean?

It means "the bottom surface"

What does "medial" mean?

It means "close to the midline"

What does "distal" mean?

It means "far"

The 31 pairs of spinal nerves are broken down into what two categories?

Dorsal and ventral roots

Because dorsal roots are sensory-related, they are ______

Because ventral roots are motor-related, they are ______

Efferent

What are the dorsal root ganglia (DRG)?

They are the cell bodies for all sensory neurons entering the spinal chord

What is a strange fact about dorsal root ganglia (DRG) regarding their location?

Their cell bodies lie outside of the central nervous system in the peripheral nervous system

What are dermatomes?

They are specific body regions for which each sensory and motor spinal nerve receives information from (and projects information to)

What is the cauda equina?

The cauda equina are long nerves from the spinal chord that dangle down and branch off to the legs

What is the visual distinction between white and grey matter in the CNS?

Grey matter will appear translucent to light and will appear grey during an autopsy/dissection while other areas are opaque to light and thus appear "white" forming white matter

What is white matter comprised of?

It is a bundle of myelinated axons running up and down the spinal cord

What is white matter called in the CNS?

It is called a tract, fasciculus or pathway

What does white matter consist of in the spinal cord?

It consists of sensory afferent fibers and motor efferent fibers

What is grey matter in the spinal cord (the bigger picture, not the specifics)?

Grey matter is unmyelinated structures in the spinal cord

What is grey matter in the spinal cord (the specifics, not the bigger picture)?

Grey matter is collections of cell bodies in the spinal cord

What region of the spinal cord does grey matter occupy?

It occupies the central region of the spinal cord (the "central grey region")

What spinal functions is the 4 lobed structure home to?

It is home to spinal sensory (dorsal) and motor (ventral) function

What is the first cell in a sensory system called?

It is the first-order neuron (1^o)

Where do the somas of all first-order neurons lie?

They lie outside of the CNS in the PNS (DRG, dorsal root ganglia)

For somatosensory systems, what does the first-order neuron synapse onto?

It synapses onto a second-order neuron (2^o) in the CNS

Where are dorsal root ganglia located (which system)?

They are located in the PNS

In sensory pathways of the spinal cord, in which system are spinal cord neurons located?

They are located in the CNS

In sensory pathways of the spinal cord, in which system are brain neurons located?

They are located in the CNS

This is the concept by which nerve fibers often cross the midline to innervate structures on the other side of the body (the left brain therefore controls the right side of the body and vice versa)

Decussation

When a projection crosses the midline, it is said to be what?

Contralateral

When a projection stays on the same side with respect to the midline, it is said to be what?

Ipsilateral

In regards to sensation from the body surface, slow activating fibers are activated by what?

Noxious (tissue damage) stimuli

With regards to sensation from the body surface, what are large, quick fibers activated by?

Any somatosensory system not involved in noxious (tissue damage) stimuli

What is the first step of sensory function?

First order mechanoreceptors enter the spinal cord and ascend ipsilaterally (same side) without synapsing and ascend in the dorsal column of the cord

What is the second step of sensory function?

The first-ordernechanoreceptors connect with a second-order neuron in the brainstem

What is the third step of sensory function?

Axons of second-order cells decussate and project onto third-order neurons in the thalamus

What are nociceptors?

They are small diameter, unmyelinated fibers which convey information about tissue damage

What is the likely transmitter in nociceptors?

Substance P

Where are first-order cells located with respect to the projection of small nociceptors?

They are located in the DRG

What is the second step of the projection of small nociceptors?

The first-order neurons synapse onto second-order cells in the dorsal horn of the spinal cord

What is the third step in the projection of small nociceptors?

Axons of the second-order cells decussate and then project to the brainstem onto third-order cells in the thalamus and reticular formation

Where does the origin for motor command lie?

It lies in the the cerebral cortex (motor cortex)

What is the final common path for motor commands?

It is the ventral horn of the spinal cord

With regards to motor pathways in the spinal cord, what do upper motor neurons do?

They project axons to contact lower motor neurons in the ventral horn of the spinal cord

With regards to motor pathways in the spinal cord, what do lower motor neurons do?

They send axons that exit the CNS and innervate the skeletal muscle

Where do the cell bodies of lower motor neurons lie?

They lie in the gray matter of the ventral horn of the spinal cord

How do axons of the lower motors neurons exit the spinal sord and onto what do they synapse?

They exit the spinal cord through the ventral roots and synapse onto skeletal muscle

The synapse between lower motor neurons and skeletal muscle can be described as what?

Exclusively cholinergic (uses acetylcholine) and uses the nicotinic acetylcholine receptor on the muscle and acts excitatory in nature

What do upper motor neurons do in regards to structural make-up and what is their function?

Upper motor neurons send two fiber bundles down either side of the spinal cord (pyramidal and extrapyramidal tracts) which activate lower motor neurons

What are the largest neurons in the mammalian brain?

Pyramidal cells

What are pyramidal tracts?

Pyramidal tracts are axons that leave upper motor neurons and cross the midline at the decussation of the pyramids and thus are contralteral in nature

Where do pyramidal tracts descend, where do they insert and what do they innervate?

The tracts descend in white matter and insert into the ventral horn of the spinal cord and innervate lower motor neurons

Where do upper motor neurons lie?

They lie in the motor cortex of the brain

Where do the primary sources of extrapyramidal motor neurons come from?

The sub-cortical (basal ganglia) and brainstem (cerebellar) nuclei

What other types of neurons do extrapyamidal cells interact with and where do these interactions take place?

They interact with pyramidal neurons (in the motor cortex) and with lower motor neurons (in the spinal cord)

Do extrapyramidal projections innervate contralaterally, ipsilaterally or both?

Both

What special capacity does the spinal cord have regarding its ability to integrate afferent input?

It can decide the appropriate motor output without having to send the signal all the way up to the sensory/motor cortexes and back down through the spinal cord

Where does most of the integration of stimuli and responses occur?

It occurs largely in the spinal cord

Fill in the blanks: Each muscle has one (blank) and is innvervated by (blank).

Sensory structures; lower motor neurons

What fibers do most fo the work in the muscle spindle organ?

Extrafusal muscle fibers

What happens when intrafusal muscle fibers in the muscle spindle organ are stretched?

Their stretch receptors are activated which causes its sensory afferents to activate synapses on the lower motor neuron which in turn activates the extrafusal fiber of the same muscle which causes the muscle to contract

What is a process such as the muscle spindle organ contraction called when only one synapse is involved?

It is called the monosynaptic reflex

Muscles exist in pairs of what?

Flexors and extensors (alpha motor neurons extend to both flexors and extensors but activate one of the other on each muscle, ex. flexor of bicep is stimulated while the extensor of tricep is stimulated)

What is the thalamus?

It is an extension of the brainstem (subcortical structure)

What is the hypothalamus?

It is ventral to the thalamus (subcortical structure)

What is the basal ganglia?

It is a subcortical structure (no other information provided)

What are the limbic lobes?

They are the olfactory bulbs and cortex, the singulate gyrus, the hippocampus and the amygdala (cortical structures)

What are the cortical structures?

They are the frontal, parietal, temporal and occipital lobes

What parts of the brain are contained within the brainstem?

The medulla, pons, reticular formation and cerebellum

What is the reticular formation?

It is comprised of 3 groups of cells that project to the forebrain

This stradles the midsagittal line in the brainstem

Raphe nuclei

This is the number 1 source of serotonin in the brain and spinal cord

Raphe nuclei

This part of the reticular formation projects rostrally and caudally

Raphe nuclei

This has a small nucleus on each side of the dorsal brainstem

Locus coeruleus (blue spot)

This is the number 1 source of norepinephrine in the brain

Locus coerulus (blue spot) of the reticular formation

This part of the reticular formation projects to cortical and subcortical regions

Locus coerulus (blue spot)

This cell type within the reticular formation makes up the ventral brainstem

Substantia Nigra (black substance)

This cell type within the reticular formation is the major source of dopamine for the brain

Substantia Nigra (black substance)

This cell type within the reticular formation projects to basal ganglia structures (mostly regarding extrapyramidal motor behavior)

Substantia Nigra (black substance)

This cell type within the reticular formation projects to the limbic medial forebrain (and appears to play a role in reward response)

Substantia Nigra (black substance)

What is important about the caudate nucleus, putamen and globus pallidus and what do these interact with?

They are important because they contain the neurons that make up the extrapyramidal motor system and they interact with pyramidal neurons in the motor cortex

Pyramidal neurons send fiber tracts directly through what?

The basal ganglia

What is an internal capsule (relating to the basal ganglia)?

It is a sheet of white matter which functions as a pyramidal projection tract

What is important to note about blood vessels in the basal ganglia?

They are very small and can become blocked or can rupture easily; hemiplegia is also a problem here

What are the hypothalamus and pituitary gland (together)?

They are a midline cluster of nuclei on the ventral surface of the forebrain and also includes a hanging gland

Where does the hypothalamus get its input from?

Limbic and brainstem structures

To where does the hypothalamus send its output?

The pituitary gland via the pituitary stalk (infundibulum)

What is important about the posterior pituitary gland?

Axon terminals from neurons in the hypothalamus release peptides into the blood here

What do cells in the anterior pituitary gland do?

They release peptides into the blood

What controls cells in the anterior pituitary gland?

The hypothalamus

Describe the thalamus

It's the most central structure in the forebrain, it's considered the most rostral extension of the brainstem and is the "old brain" region that communicates with the brainstem and cortex

Describe the neuronal input and output of the thalamus

The thalamus receives projections from many sensory modalities and projections information about that sensation to specific regions of the cortex

What kind of information do lateral geniculate nuclei relay?

Visual information

What kind of information do medial geniculate nuclei relay?

Auditory information

What kind of information do ventralposterior lateral and medial nuclei relay?

Somatosensory information

What are the "crests and valleys" that appear on the structure of the brain called?

Gyrus and sulcus (respectively)

What is the boundary of the frontal lobe?

It is all cortex rostral to the central sulcus

What is the precentral gyrus?

It is immediately rostral to the central sulcus and is the **primary motor cortex**

What are some smaller details about the frontal lobe regarding its positioning and size in humans?

The rostral pole probably plays a role in ideation and cognition while it is larger and more elaborate in humans than in other primates

What is the boundary of the parietal lobe in the brain?

It is the cortex caudal to the central sulcus

What is the postcentral gyrus?

It is immediately caudal to the central sulcus and is the **primary somatosensory cortex**

What major function does the temporal lobe play?

It is the primary auditory cortex