ANAT 321 Midterm

CNS

The portion of the nervous system which is composed of the brain and spinal cord

Modality

A quality or sense (e.g., somatic sensation)

Submodality

The subcategories of a given sense (e.g., warmth, heat, fine touch, vibration)

Somatic sensory system

Encodes sensory information about the skin surface (e.g., touch, vibration, temperature, pain) and sensory information from inside the body (e.g., visceral pain)

Dorsal column medial lemniscal

The pathway involved in fine touch and proprioception (somatic sensory pathway)

Anterolateral

The pathway involved in conveying pain and temperature information to the cortex

Sensory transduction

The first step in sensory processing which transforms sensory information from the external (or internal) environment into opening (or closing) of ion channels in receptor cells

Primary sensory fibers

The first neurons to be activated in the sensory pathway which have sensory receptors at their endings

Sensory receptors

Specialized endings of sensory fibers which act as filters, extracting specific forms of sensory information and ignoring others

Slowly adapting

Type of receptors which fire for as long as pressure is applied (throughout the stimulus. They are specialized in detecting constant pressure at the skin surface

Rapidly adapting

Type of receptors which only depolarize at the onset and end of the stimulus. They are specialized in detecting vibrations and texture

Free nerve endings

Type of nerves that don’t end in specialized structures are are specialized in depolarizing due to mechanical pain or temperature

Labeled line

A given axon which only conveys information regarding a specific sensory submodality

Combinatorial processing

Perceived sensations are typically caused by activation of multiple receptor types and integration of multiple parallel channels by the brain

Afferent

Incoming information (e.g., primary somatic sensory fibers)

Efferent

Outgoing information (e.g., motor neurons)

Ascending

Heading up to higher levels of the nervous system (e.g., sensory afferents)

Descending

Heading down from higher levels of the nervous system (e.g., corticospinal projections)

Ipsilateral

On the same side of the body

Contralateral

On the opposite side of the body

Receptive field

The region where stimulus will activate the neurons and excite the cell. As you move up the sensory pathway, these get larger

High acuity

Regions where the receptive fields are small and therefore the neurons are closer together. These areas have high specificity

8

The number of cervical segments

12

The number of thoracic segments

5

The number of lumbar segments

5

The number of sacral segments

1

The number of coccygeal segments

Lumbar cistern

The space below the caudal end of the spinal cord filled with CSF and the nerves coming up from the lower body

Cauda equina

Bundle of nerves coming up to the spinal cord from the lower body

Foramen magnum

The area where the spinal cord enters the skull to form the medulla (the most caudal part of the brainstem)

Gray matter

Regions of the nervous system consisting mainly of neuronal cell bodies, dendrites, and synapses. This is where neurons interact with each other

White matter

Bundles of myelinated axons

Dorsal horn

Portion of the spinal cord gray matter which is mainly involved in sensory function. This is where the cell bodies of second order neurons in the anterolateral pathway are located

Ventral horn

Portion of the spinal cord gray matter which is mainly involved in movement. This is where the cell bodies of motor neurons are located

Dorsal root ganglion

An organized cluster of cell bodies in the peripheral nervous system containing the cell bodies of somatic sensory neurons

Nucleus

An organized clusters of neuronal cell bodies in the central nervous system

Nerve

A bundle of axons in the peripheral nervous system. Contains sensory axons and the axons of motor neurons

Dermatome

Region of the body that is innervated by a specific pair of spinal nerves

Intermediate region

Region of the spinal cord which contains interneurons (connect sensory and motor neurons) and autonomic neurons (preganglionic neuronal cell bodies of the sympathetic system)

Dorsal column

Region of the white matter along which primary afferents for fine touch ascend to the brainstem

Anterolateral column

Region of the white matter of the spinal cord along which the second order neurons of the pain and temperature pathway ascend to the thalamus

Medial

Region of the dorsal column innervating the legs and region of the anterolateral column innervating the arms

Lateral

Region of the dorsal column innervating the arms and region of the anterolateral column innervating the legs

Central pattern generators

Rhythmic movements like walking whose intrinsic circuitry is located within the spinal cord

Fiber tract

Bundle of axons in the central nervous system

Projections

Axons that extend from one region of the nervous system to another

Brainstem

Area of the nervous system which is subdivided into the midbrain, pons, and medulla

Fasciculus gracilis

Axons of the dorsal columns representing the legs in the caudal part of the medulla (dorsal most region of the area)

Facilis cuneatus

Axons in the dorsal columns representing the arms in the caudal regions of the medulla

Spinothalamic tract

Otherwise known as the anterolateral column. Contains axons of second order neurons involved in the pain and temperature pathway

Dorsal column nuclei

Cell bodies of the second order nuclei of the fine touch and proprioception pathway located in the medulla

Nucleus gracilis

Cell bodies of the second order neurons which receive input regarding fine touch and proprioception of the legs

Nucleus cuneatus

Cell bodies of the second order neurons which receive input regarding fine touch and proprioception in the arms

Medial lemniscus

Fiber tracts of the axons of second order neurons in fine touch and proprioception pathway heading up to the thalamus (dorsal = arms; ventral = legs). This tract fans out as we move rostrally up the brainstem

Reticular formation

Central core of gray matter in the brainstem which includes the cranial nerve nuclei as well as dendrites and synapses. Invovled in stereotypes motor responses (facial expressions), autonomic functions (parasympathetic), and ascending arousal

Periaqueductal gray

Area connected to regions of the brainstem involved in autonomic, somatic and behavioral responses and to higher brain regions involved in fear. It coordinates the behavioral responses of fear

Ascending arousal system

There are ascending brainstem projections to the cortex that are involved in keeping it awake (dorsal go through the thalamus, ventral go directly to the cortex)

Norepinephrine

Neurotransmitter whose neurons orriginate in the locus coeruleus and project to virtually the entire brain and spinal cord. The ascending projections are involved in sleep-wake cycles, arousal and attention

Serotonin

Neurotransmitter whose neurons originate in the raphe nuclei and project throughout the brain and spinal cord. There may be a correlation between this neurotransmitter and mood

Dopamine

Neurotransmitter whose neurons originate in the substantia nigra (movement; project to the basla ganglia) and the ventral tegmental area (involved in learning and association; project to the cortex)

Acetylcholine

Neurotransmitter whose neurons originate in the basal forebrain and project to the cortex, hippocampus, and amygdala. They play a modulatory role in sleep wake cycles and attention when synapsing on metabotropic muscarinic receptors

Convergence

When many primary neurons (typically from one part of the body) synapse on a single second order neuron

Divergence

When the axon of one primary neuron branches out to innervate multiple second order neurons in the pathway

Lateral inhibition

Allows a strong signal to pass through but filters out weak surrounding signals (sharpens contrast of sensory signals). Strongly activated neurons activate inhibitory interneurons which dampen the signal of weakly activated neurons

Coronal

Sectioning of the brain that divides it into the anterior (rostral) and posterior (caudal) sections

Horizontal

Sectioning of the brain that divides it into the dorsal and ventral sections

Sagittal

Sectioning of the brain that divides it into the right and left hemispheres (mid)

Specific relay

Type of nuclei of the thalamus that convey primary sensory modalities to the primary sensory cortex

Association

Type of nuclei of the thalamus that are interconnected with regions of association cortex and receive their driver inputs from the cortex (layer 5)

Intralaminar

Type of nuclei of the thalamus the project diffusely to many regions of the cortex as well as subcortical structures such as the basal ganglia

Feedforward

Projections that are moving up the sensory pathway (drivers)

Feedback

Projections that are going back down the sensory pathway (modulators)

Driver inputs

Cause action potential activity in the neurons on which they synapse

E.g., thalamic nuclei → 4th layer of the cortex

5th layer of the cortex → association nuclei

Modulatory inputs

Axons which alter the physiology of thalamic neurons (don’t excite them). They can alter the AP threshold or resting membrane potential

E.g., brainstem → thalamic nuclei (neuromodulators)

6th layer of the cortex → thalamic nuclei

Transmission mode

Used in wakefulness. In this mode thalamic neurons fire single action potentials that faithfully relay sensory inputs. Resting potential is more positive than -65 mV

Bursting mode

Thalamic neurons firing bursts of 3-8 action potentials, separated by quiet periods lasting 100s of ms. Resting membrane potential is more negative than -65 mV

Internal capsule

Fiber tract which contains information from the cerebral cortex, axons from the thalamus to the cortex, and axons from the brainstem to the cortex

Gyri

Pl. The folds (mountains) of the cortex

Sulci

Pl. The grooves between the folds of the cortex

Central sulcus

Middle of the three parallel sulci that move from the top of the brain towards the lateral sulcus

Lateral sulcus

Deep groove that splits the C of the cortex (perpendicular to the central sulcus)

Frontal lobe

Lobe anterior to the central sulcus and dorsal to the lateral sulcus. Involved in movement (caudal) and planning behavior (rostral)

Occipital lobe

Most caudal lobe of the cortex. Involved in primary visual processing

Temporal lobe

Ventral to the lateral sulcus. Involved in learning and memory. Contains the hippocampus

Parietal lobe

Dorsal to the lateral sulcus; Posterior to the central sulcus; Rostral to the occipital lobe. Involved in high order sensory processing

Longitudinal fissure

Deep groove that separates the two cerebral hemispheres

Limbic lobe

Lobe only seen on the medial surface of the cortex. Bounded by the cingulate sulcus

Corpus collosum

White matter which contains the axons connecting the two cerebral hemispheres, allowing them to interact with each other

Area 17

Brodmann’s area which contains the primary visual cortex

Area 18

Brodmann’s area which contains the association visual cortex (higher order sensory processing) = V2

Area 4

Brodmann’s area which contains the primary motor cortex

Molecular layer (I)

Layer of cortex which does not contain many cell bodies but does contain a large amount of synapses

External granule layer (II)

Layer of the cortex which contains granule cells. Involved in making feedforward projections to other regions of the cortex (association) and deep layers

External pyramidal layer (III)

Layer of the cortex which contains pyramidal cells). Involved in making feedforward projections to other regions of the cortex (association) and deep layer

Internal granule layer (IV)

Cortical layer which is the main recipient of afferent inputs from the thalamus. Made up of excitatory stellate cells. Neurons project to superficial layers in the same column

Internal pyramidal layer (V)

Cortical layer with large pyramidal neurons which project to the basal ganglia, thalamus (driver: association nuclei), brainstem and spinal cord

Multiform layer (VI)

Cortical layer whose cell bodies initiate feedback projections which head to the thalamus

Cortical column

Fundamental functional module of the cortex which contains thousands of neurons responding to the same type of stimulus at the same location on the body. The neurons are highly interconnected and show similar response properties

Primary motor cortex

Precentral gyrus. Its outputs control voluntary movement

Primary auditory cortex

Superior temporal gyrus. Receives inputs from the medial geniculate nucleus