ANAT1012: Nervous System and Motor Control

A complete 157-question study deck reviewing somatosensory systems, vision, pyramidal and extrapyramidal motor pathways, the basal ganglia, cerebellar circuitry and functions, and the limbic system and memory.

What is the usual neuron sequence for conscious sensation from the body?

Receptor → first-order neuron with its cell body in the dorsal root ganglion (DRG) → second-order neuron → thalamus → third-order neuron → postcentral gyrus (primary somatosensory cortex).

Where is the cell body of a first-order body sensory neuron?

In the dorsal root ganglion (DRG). The neuron is pseudounipolar: one branch reaches the receptor and the other enters the CNS.

Which sensations travel mainly in the dorsal column–medial lemniscus (DCML) pathway?

Discriminative touch, pressure, vibration, and conscious proprioception (awareness of body position and movement).

Which sensations travel mainly in the anterolateral system?

Pain, temperature, itch, and crude touch.

Trace the DCML pathway from a receptor in the foot to the cortex.

Foot receptor → DRG → enters spinal cord → ascends ipsilaterally in fasciculus gracilis → synapses in nucleus gracilis in caudal medulla → second-order fibres cross → medial lemniscus → VPL thalamus → third-order fibres through posterior limb of internal capsule → postcentral gyrus.

Trace the DCML pathway from a receptor in the hand to the cortex.

Hand receptor → DRG → enters spinal cord → ascends ipsilaterally in fasciculus cuneatus → synapses in nucleus cuneatus in caudal medulla → second-order fibres cross → medial lemniscus → VPL thalamus → posterior limb of internal capsule → postcentral gyrus.

What does the fasciculus gracilis carry, and where is it in the dorsal column?

Information from the lower trunk and lower limb. It is the medial part of the dorsal column.

What does the fasciculus cuneatus carry, and where is it in the dorsal column?

Information from the upper trunk and upper limb. It lies lateral to fasciculus gracilis and is present above about T6.

Where does the DCML pathway cross to the other side?

In the caudal medulla, after the first-order neuron synapses in nucleus gracilis or nucleus cuneatus.

What is the medial lemniscus?

The ascending bundle formed by crossed second-order DCML fibres in the brainstem.

A left DCML lesion occurs in the spinal cord. Which side of the body loses vibration below the lesion, and why?

The left side. DCML fibres have not crossed yet while ascending in the spinal cord, so they are still on the same side as the body information they carry.

A right DCML lesion occurs in the brainstem above the medullary crossing. Which body side loses vibration, and why?

The left side. The fibres from the left body have already crossed in the medulla and now ascend on the right.

What does it mean to ask whether a lesion is before or after a pathway’s crossing?

It asks whether the fibres carrying information from the affected body side have switched sides by the time they reach the lesion. Before crossing they are on the same side; after crossing they are on the opposite side.

Trace the anterolateral pathway from a painful stimulus in the left foot to the brain.

Receptor → DRG → enters left dorsal root → may travel 1–3 segments in Lissauer’s tract → synapses in dorsal horn → second-order axon crosses through anterior white commissure → ascends on the right in the anterolateral cord → thalamus → third-order neuron to postcentral gyrus.

Where does the anterolateral pathway cross?

In the spinal cord, through the anterior white commissure, usually within a few segments of entry.

What is Lissauer’s tract and why does it matter for lesion patterns?

A small pathway where some first-order pain and temperature fibres travel up or down about 1–3 spinal levels before synapsing in the dorsal horn. It helps explain why pain/temperature loss from a spinal lesion may begin a few levels below it.

Where do many first-order anterolateral fibres synapse?

In the dorsal horn, including laminae I and II (substantia gelatinosa), a region involved in pain processing and modulation.

A left anterolateral tract lesion in the spinal cord affects pain and temperature from which body side below the lesion?

Usually the right side, because pain/temperature fibres from the right body cross to the left before ascending in the left anterolateral tract.

What does a unilateral spinal cord lesion typically do to DCML versus pain/temperature sensation below it?

It can cause same-side loss of DCML sensations below the lesion and opposite-side loss of pain/temperature beginning a few segments below it. The two pathways cross at different places.

What is somatotopy?

An orderly map in which neighbouring body regions tend to have correspondingly organised fibres in pathways, nuclei, and cortex.

How are fibres arranged within the dorsal columns from sacral to cervical levels?

Sacral fibres are medial; fibres from progressively higher levels are added more laterally, with cervical fibres lateral to sacral fibres.

How are fibres arranged broadly in the anterolateral tract?

Sacral fibres are more lateral and cervical fibres more medial.

Where is the primary somatosensory cortex and how is the body represented there?

In the postcentral gyrus of the parietal lobe. The leg is represented medially, then trunk, arm/hand, and face more laterally; body parts needing finer sensory discrimination take more cortical area.

What does the secondary somatosensory area help you do?

Combine and interpret touch and related sensory information, such as recognising an object by touch.

What is astereognosis?

Difficulty recognising a familiar object by touch despite being able to feel its features; it can follow damage to somatosensory association areas.

What does the posterior parietal association cortex do?

Combines sensory information across modalities, such as touch and vision, to guide attention and interaction with space.

Which broad arteries supply the medial versus lateral primary sensory cortex?

The anterior cerebral artery (ACA) mainly supplies the medial cortex, including much of the leg area. The middle cerebral artery (MCA) mainly supplies the lateral cortex, including much of the face and arm areas.

Which arteries supply the dorsal columns of the spinal cord versus much of the rest of it?

Posterior spinal arteries supply the dorsal columns. The anterior spinal artery supplies much of the remaining spinal cord, with segmental contributions.

What is the face’s equivalent of the body’s ascending somatosensory pathways?

Trigeminothalamic pathways, which carry facial sensation through the trigeminal system to the thalamus and cortex.

What do spinothalamic, spinoreticular, spinomesencephalic, and spinohypothalamic routes broadly contribute?

Spinothalamic: conscious pain and localisation. Spinoreticular: alertness/attention. Spinomesencephalic: pain modulation, including via PAG. Spinohypothalamic: autonomic responses to pain.

What is the visual field?

The part of the environment visible to a person when their gaze is directed at a point.

How is the image on the retina oriented compared with the visual field?

It is inverted and reversed: the upper field lands on the lower retina, the lower field on the upper retina; temporal field lands on nasal retina and nasal field on temporal retina.

What are the photoreceptors, and what are rods and cones broadly specialised for?

Rods and cones detect light. Rods are more useful in dim light; cones support colour and finer detail, especially around the fovea/macula.

What is the neuron sequence in the retina?

Photoreceptors synapse on bipolar cells (first-order neurons), which synapse on retinal ganglion cells (second-order neurons). Ganglion-cell axons form the optic nerve.

Trace the main conscious visual pathway.

Retina → optic nerve → optic chiasm → optic tract → lateral geniculate nucleus (LGN) of thalamus → optic radiations → primary visual cortex around the calcarine sulcus in the occipital lobe.

Which retinal fibres cross at the optic chiasm?

Fibres from the nasal half of each retina cross. Fibres from the temporal half remain on the same side.

What visual-field information does each optic tract carry?

The contralateral visual field from both eyes. For example, the right optic tract carries information about the left visual field.

Where do the conscious visual pathway fibres synapse in the thalamus?

In the lateral geniculate nucleus (LGN).

Where is the primary visual cortex?

In the occipital lobe around the calcarine sulcus. The rest of the occipital lobe includes secondary visual areas that help interpret what is seen.

What are the superior colliculus and pretectal area’s visual roles?

They receive some retinal input and contribute to visual reflexes and orienting responses rather than the main route for conscious visual perception.

Which visual field is represented by Meyer’s loop in the temporal lobe?

The upper visual field. It lands on the lower retina, and those fibres travel through the lower optic radiations, including Meyer’s loop.

What visual field is carried by the more superior optic radiations in the parietal region?

The lower visual field, which is represented on the upper retina.

What does ‘homonymous’ mean in a visual field deficit?

The same side of the visual field is lost in both eyes.

What does ‘hemianopia’ mean?

Loss of half of the visual field.

What does ‘quadrantanopia’ mean?

Loss of one quarter of the visual field.

What is a contralateral homonymous hemianopia?

Loss of the same half of the visual field in both eyes, on the side opposite a brain lesion.

What field loss follows damage to one optic nerve?

Loss of vision in that eye (monocular anopia), because that nerve carries all visual input from that eye.

What field loss follows a lesion in the centre of the optic chiasm, and what is a common cause?

Bitemporal hemianopia: loss of the outer visual fields in both eyes, because crossing nasal-retinal fibres are affected. A pituitary tumour can press on the chiasm.

What field loss follows an optic tract or LGN lesion?

Contralateral homonymous hemianopia, because the tract/LGN carries the opposite visual field from both eyes.

What field loss follows a lesion of the right Meyer’s loop?

A left superior quadrantanopia (loss of the upper left quarter of the visual field).

What field loss follows a lesion of the right parietal optic radiations?

A left inferior quadrantanopia (loss of the lower left quarter of the visual field).

What field loss can follow a visual-cortex lesion, and what is macular sparing?

Often a contralateral homonymous hemianopia. Macular sparing means central vision is relatively preserved despite loss of much of the surrounding field.

Which arteries are important for the visual pathway?

The anterior choroidal artery supplies the optic tract, LGN, and parts of the optic radiations. The posterior cerebral artery (PCA) supplies the primary and secondary visual cortices.

How do you work out a visual field lesion rather than memorising a picture?

Identify which retinal fibres pass through the lesion, whether they have crossed at the chiasm, and which part of the visual field those fibres represent.

What is the lower motor neuron’s role?

It is the final neural route to skeletal muscle. Body LMNs are in the spinal ventral horn; many head/neck LMNs are in brainstem cranial-nerve motor nuclei.

What is an upper motor neuron (UMN)?

A neuron from the cerebral cortex or brainstem that descends to influence LMNs, directly or through interneurons.

What is the difference between alpha and gamma motor neurons?

Alpha motor neurons activate the main force-producing muscle fibres. Gamma motor neurons adjust muscle-spindle sensitivity so length feedback remains useful during contraction.

Why is the LMN called the final common pathway?

Commands from cortex, brainstem, reflexes, and spinal circuits all ultimately need to influence an LMN to activate skeletal muscle.

What does the prefrontal cortex contribute to movement?

Goals, decisions, context, and executive planning that help determine what action to take.

What does the premotor cortex contribute to movement?

It prepares actions using external sensory cues, such as visual information about a target; this is a sensorimotor transformation.

What does the supplementary motor area (SMA/SMC) contribute to movement?

Planning self-generated actions and learned sequences, mental rehearsal, and bilateral coordination.

What does primary motor cortex (M1) contribute to movement?

It contributes strongly to executing voluntary movement through descending corticospinal and corticonuclear pathways.

Where is M1, and what is its body map called?

M1 is in the precentral gyrus, immediately anterior to the central sulcus. Its body map is the motor homunculus.

What is the broad arrangement of the motor homunculus?

Leg is represented medially; trunk, arm/hand, and face are progressively more lateral. Body parts needing finer control have more cortical representation.

What are the two main pyramidal pathways?

Corticospinal (cortex to spinal cord) and corticonuclear/corticobulbar (cortex to cranial-nerve motor nuclei in the brainstem).

Trace the corticospinal pathway from cortex to spinal cord.

Motor cortex → corona radiata → posterior limb of internal capsule → crus cerebri → base of pons → medullary pyramids → spinal cord.

Which internal-capsule regions carry corticospinal and corticonuclear fibres?

Corticospinal fibres mainly pass through the posterior limb. Corticonuclear fibres mainly pass through the genu.

Where do most corticospinal fibres cross?

At the pyramidal decussation in the caudal medulla.

What is the lateral corticospinal tract and what does it mainly control?

The roughly 85–90% of corticospinal fibres that cross in the medulla and descend contralaterally. It is especially important for skilled limb movement, including distal movement.

What is the anterior corticospinal tract and what does it mainly control?

The smaller group that does not cross at the medulla. It descends mainly anteriorly and influences axial/proximal muscles for posture; many fibres cross near their spinal target or act bilaterally.

Why can a right motor-cortex lesion weaken the left body?

Most corticospinal fibres cross in the medulla, so the right cortex predominantly controls the left side of the body.

Where do corticonuclear fibres go?

They branch from the descending cortical pathway in the brainstem and synapse on cranial-nerve motor nuclei that control head and neck muscles.

Do cranial-nerve motor nuclei usually receive input from one or both cerebral hemispheres?

Many receive bilateral cortical input. Some, such as the lower facial motor region and much of the genioglossus supply, have stronger contralateral input.

What does the medial longitudinal fasciculus (MLF) do for eye movements?

It links brainstem eye-movement nuclei with one another and vestibular nuclei, helping coordinate the two eyes and stabilise gaze with head movement.

Where do pyramidal pathways travel in the brainstem?

Predominantly through the anterior basis: crus cerebri in the midbrain, base of pons, and medullary pyramids.

What are the basis, tegmentum, and tectum of the brainstem?

Basis: anterior part, containing pyramidal fibres. Tegmentum: central region with many nuclei, sensory pathways, and extrapyramidal fibres. Tectum: dorsal roof of the midbrain, including the colliculi.

What are the superior and inferior colliculi broadly involved in?

Superior colliculus: visual orienting and related reflexes. Inferior colliculus: auditory processing and reflex pathways.

What are the usual signs of an UMN lesion?

Weakness, increased tone, brisk reflexes, slower/less marked wasting than an LMN lesion, and sometimes an extensor plantar (Babinski) response.

What are the usual signs of an LMN lesion?

Weakness, reduced tone, reduced reflexes, more rapid/marked muscle wasting, and possibly fasciculations.

What is the extensor plantar or Babinski response?

When stroking the sole causes the big toe to extend upward, sometimes with fanning of the other toes. It can be normal in infants (the corticospinal pathway is not fully developed yet), in adults it can indicate corticospinal/UMN dysfunction.

What does ‘extrapyramidal’ mean in this lecture series?

Primarily brainstem-originating descending motor pathways that support posture, balance, muscle tone, orienting, gait, and automatic adjustments. They complement voluntary cortical commands.

Name the four major extrapyramidal spinal tracts and their origins.

Rubrospinal: red nucleus. Tectospinal: superior colliculus/tectum. Reticulospinal: reticular formation. Vestibulospinal: vestibular nuclei.

What is the rubrospinal tract’s course and course-level function?

It originates in the midbrain red nucleus, crosses near its origin, descends in the lateral cord near the lateral corticospinal tract, and is described as flexor-biased, especially for upper-limb influence.

What is an important caveat about the rubrospinal tract in humans?

It is less prominent than in many other mammals, and its exact role in human movement is not fully settled. The flexor-biased upper-limb description is a useful course summary.

What is the tectospinal tract’s course and function?

It originates in the superior colliculus, mostly crosses in the midbrain, descends to cervical levels, and helps orient the head/neck toward relevant visual or other sensory stimuli.

What is the reticulospinal tract’s course and function?

It originates in pontine/medullary reticular formation, descends mainly bilaterally through anterior/ventral regions to many spinal levels, and supports posture, gait, and coordinated adjustments, often with extensor/antigravity bias.

What is the lateral vestibulospinal tract’s function and laterality?

It arises from the lateral vestibular nucleus, mainly descends ipsilaterally to many spinal levels, and facilitates antigravity extensors to help maintain stance and balance.

What is the medial vestibulospinal tract’s function and destination?

It arises from medial vestibular nuclei, acts bilaterally, mainly reaches cervical levels, and stabilises head/neck position during movement.

How is the vestibulo-ocular reflex different from vestibulospinal output?

Vestibulo-ocular reflex moves the eyes to stabilise gaze as the head moves, through brainstem eye-movement connections. Vestibulospinal output influences spinal motor pathways for posture and head/body stability.

What is the difference between spinal reflexes and supraspinal postural responses?

Spinal reflexes use spinal inputs and local circuits, so they are fast and stereotyped. Brainstem/supraspinal responses can integrate vestibular, visual, proprioceptive, cortical, and cerebellar information and coordinate many muscles adaptively.

What is the dorsolateral motor pathway group associated with?

Lateral corticospinal and rubrospinal pathways; broadly more associated with limb movement and lateral LMN pools, especially distal control.

What is the ventromedial motor pathway group associated with?

Anterior corticospinal, reticulospinal, vestibulospinal, and tectospinal pathways; broadly more associated with axial/proximal muscles, posture, balance, and bilateral control.

What is decorticate posturing in the course-level explanation?

A lesion above the red nucleus removes cortical influence, while red-nucleus flexor-biased influence remains for the arms; extensor-biased brainstem influence remains prominent in the legs.

What is decerebrate posturing in the course-level explanation?

A lesion at or below the red-nucleus level removes more red-nucleus influence, leaving extensor-biased brainstem influences relatively unopposed in both arms and legs.

What is the basal ganglia’s broad role in motor control?

Help select and regulate appropriate action plans, facilitate the desired action, suppress competing actions, and regulate movement amplitude and timing.

Do the basal ganglia directly connect to spinal LMNs?

No. They influence cortex and brainstem circuits; their major motor loop returns through the thalamus to cortex.

Which structures are the main functional basal ganglia components in this course?

Striatum (caudate and putamen), GPe, GPi, subthalamic nucleus (STN), and substantia nigra pars compacta (SNc) and pars reticulata (SNr).

What is the striatum and why does it look striped?

The caudate and putamen together. In humans they are separated by internal-capsule fibres, with connecting bridges that give a striped appearance.

What are the major input and output regions of the motor basal ganglia loop?

The striatum is the major input region, receiving substantial cortical input. GPi and SNr are major output nuclei.

What neurotransmitters are most important for understanding the direct/indirect diagrams?

Glutamate is generally excitatory; GABA is inhibitory. Dopamine can have different effects depending on receptor, especially D1 versus D2.