Principles of Neuroanatomy

Question 1

What are the 3 planes and what axis do they describe?

Answer 1

Coronal/Frontal - uses the anterior/posterior plane
Sagittal - uses medial/lateral plane
Axial plane - uses the superior/inferior plane

Question 2

Why do rostral/caudal mean different things for the brain and spinal cord?

Answer 2

Rostral means towards the nose and caudal means towards the tail. In animals that swim or walk on all fours these orientations are consistent, but in
humans they shift at the brainstem-diencephalon junction. At the level of the spinal cord, rostral points up towards the head while caudal points down
towards the end of the cord.
In the brain, however, rostral points towards the anterior part of the brain while caudal
points toward the posterior part of the brain.

Question 3

What is the CNS?

Answer 3

The central nervous system consists of the brain and spinal cord, lying within the protection of the cranium and vertebral column, respectively. It is the most complex part of the nervous system, containing the majority of nerve cell bodies and synaptic connections.

Question 4

What is the PNS?

Answer 4

The peripheral nervous system constitutes the link between the CNS and structures in the periphery of the body, from which it receives sensory information and to which it sends controlling impulses. The peripheral nervous system consists of nerves joined to the brain and spinal cord (cranial and spinal nerves) and their ramifications within the body.

Question 5

Describe structure of PNS

Answer 5

Spinal nerves serving the upper or lower limbs coalesce to form the brachial or lumbar plexus , respectively, within which fibres are redistributed into named peripheral nerves . The PNS also includes many peripherally located nerve cell bodies, some of which are aggregated within structures called ganglia.

Question 6

What are the two halves of the sensory nervous system?

Answer 6

Neurones that are concerned with detecting changes in the external environment, or with the control of movement, are collectively referred to as the somatic nervous system. Neurones that detect changes in, and control the activity of, the viscera are collectively referred to as the autonomic nervous system. Somatic and autonomic components are present in both the central and peripheral nervous systems.

Question 7

How is the autonomic nervous system divided?

Answer 7

The autonomic nervous system is divided into two anatomically and functionally distinct parts, namely the sympathetic and parasympathetic divisions, which generally have opposing (antagonistic) effects on the structures that they innervate. The autonomic nervous system innervates smooth muscle, cardiac muscle and secretory glands. Responsible for homeostasis that controls internal environment.

Question 8

What are the types of neurones?

Answer 8

Nerve cells that carry information from peripheral receptors to the CNS are referred to as afferent neurones. If the information they carry reaches consciousness, they are also called sensory neurones. Efferent neurones carry impulses away from the CNS and if they innervate skeletal muscle to cause movement, they are also called motor neurones. The vast majority of neurones, however, are located entirely within the CNS and are referred to as interneurones.

Question 9

What is grey matter?

Answer 9

Regions relatively enriched in nerve cell bodies (e.g. the central portion of the spinal cord and the surface of the cerebral hemisphere) are referred to as grey matter .

Question 10

What is white matter?

Answer 10

Regions contain mostly nerve processes (usually axons). These are often myelinated (ensheathed in myelin), which confers a paler coloration – hence the term white matter.

Question 11

What are nuclei and pathways?

Answer 11

Nerve cell bodies with similar anatomical connections and functions (e.g. the motor neurones innervating a group of related muscles) tend to be located together in groups called nuclei. Similarly, nerve processes sharing common connections and functions tend to follow the same course, running in pathways or tracts

Question 12

What is decussation and what are its implications?

Answer 12

Pathways conveying sensory information to a conscious level (the cerebral hemisphere) cross over, or decussate, from one side of the CNS to the other. The same is true of descending pathways from the cerebral hemisphere that control movement. Therefore in general, each cerebral hemisphere perceives sensations from, and controls the movements of, the contralateral side of the body.

Question 13

What are the meninges?

Answer 13

CNS is entirely ensheathed by three concentric layers of membranes. The outermost membrane is the dura mater , a tough, fibrous coat that surrounds the brain and spinal cord like a loose-fitting bag. Beneath the dura lies the arachnoid mater, the two being separated by a thin subdural space.
The arachnoid is a translucent, collagenous membrane that, like the dura, loosely envelops the brain and spinal cord.
The innermost of the meninges is the pia mater , a delicate membrane of microscopic thickness that is firmly adherent to the surface of the brain and spinal cord, closely following their surface contours.
Between the arachnoid and pia is the subarachnoid space through which cerebrospinal fluid (CSF) circulates.

Question 14

How is the dura arranged?

Answer 14

The spinal dura and much of the cranial dura are separate from the periosteum, which forms the inner lining of the surrounding bones. At certain locations, however, such as on the floor of the cranial cavity, the dura and periosteum are fused and the cranial dura is tightly adherent to the interior surface of the skull.

Question 15

What are the falx cerebri and tentorium cerebelli?

Answer 15

These are large sheets (or reflections) of dura which project into the cranial cavity, incompletely dividing it into compartments. the falx cerebri lies in the sagittal plane between the two cerebral hemispheres. Its free border lies just above the corpus callosum. The other dural sheet, the tentorium cerebelli, is oriented approximately horizontally, lying beneath the occipital lobes of the cerebral hemispheres and above the cerebellum. The tentorium cerebelli is continuous with the posterior part of the falx cerebri.

Question 16

How are the dural venous sinuses created?

Answer 16

Dura mater can be regarded as consisting of two layers. These are fused together except in certain locations, where they become separated to form spaces, the dural venous sinuses, which serve as channels for the venous drainage of the brain. Important dural sinuses occur:

1. On the floor of the cranial cavity
2. Along the lines of attachment of the falx cerebri and tentorium cerebelli to the interior of the skull (superior sagittal sinus and transverse sinus)
3. Along the line of attachment of the falx cerebri and tentorium cerebelli to one another (straight sinus)

Question 17

How is the brain supplied with blood?

Answer 17

The brain is supplied with arterial blood by the internal carotid and vertebral arteries , which anastomose to form the circulus arteriosus (circle of Willis) on the base of the brain. The arteries and veins serving the CNS run for part of their course within the subarachnoid space.

Question 18

How is the spinal cord supplied with blood?

Answer 18

The spinal cord is supplied by vessels arising from the vertebral arteries, reinforced by radicular arteries derived from segmental vessels.

Question 19

How are the meninges supplied with blood?

Answer 19

The meninges are supplied by a number of vessels, the most significant intracranial one being the middle meningeal artery, which ramifies extensively between the skull and dura mater overlying the lateral aspect of the cerebral hemisphere.

Question 20

Where does the spinal cord lie?

Answer 20

The spinal cord lies within the vertebral (spinal) canal of the vertebral column and is continuous rostrally (superiorly) with the medulla oblongata of the brainstem. The spinal cord receives information from, and controls, the trunk and limbs.

Question 21

Describe how spinal nerves are attached to the spine

Answer 21

31 pairs of spinal nerves are attached to the cord at intervals along its length. Contain afferent and efferent nerve fibres connecting with structures in the periphery. Near to the cord, the spinal nerves divide into dorsal (posterior) and ventral (anterior) roots, which attach to the cord along its dorsolateral and ventrolateral borders, respectively

Question 22

What is the purpose of the dorsal and ventral roots of the spinal nerves?

Answer 22

The dorsal roots carry afferent nerve fibres, the cell bodies of which are located in dorsal root ganglia.
The ventral roots carry efferent nerve fibres, the parent cell bodies of which lie within the spinal grey matter.

Question 23

How do spinal nerves leave the vertebral canal

Answer 23

Through small apertures, called intervertebral foramina, which are located between adjacent vertebrae.

Question 24

How are the lumbar and sacral nerves different?

Answer 24

Because of the difference in the rates of growth of the spinal cord and vertebral column during development, the spinal cord in the adult does not extend for the full length of the vertebral canal, but ends at approximately the level of the intervertebral disc between L1 and L2 vertebrae. The lumbar and sacral spinal nerves, therefore, descend in a leash-like arrangement, called the cauda equina, to reach their exit foramina.

Question 25

Describe what can be seen in a transverse section through the spinal cord

Answer 25

Can see the roots attaching to the spinal cord. At its centre, central canal contains the cylindrical spinal cord. The relative separation of cell bodies from nerve fibres confers a characteristic ‘H’ shape to the central core of grey matter that surrounds the central canal. Four projections of the central grey matter extend dorsolaterally and ventrolaterally towards the lines of attachment of the dorsal and ventral roots of the spinal nerves. These projections are known as the dorsal horns and ventral horns.

Question 26

What is the purpose of the dorsal and ventral horns?

Answer 26

The dorsal horn is the site of termination of numerous afferent neurones, conveying impulses from sensory receptors throughout the body, and is the site of origin of ascending pathways carrying sensory impulses to the brain. The ventral horn contains motor neurones that innervate skeletal muscle.

Question 27

What is the lateral horn and where is it found?

Answer 27

At thoracic and upper lumbar levels of the cord only, smaller collection of cell bodies comprises the lateral horn. This contains preganglionic neurones belonging to the sympathetic division of the autonomic nervous system.

Question 28

What does the periphery of the spinal cord consist of?

Answer 28

White matter that contains longitudinally running nerve fibres. These are organised into ascending tracts and descending tracts. Ascending tracts carry information derived from the trunk and limbs to the brain. Descending tracts are the means by which the brain controls the activities of neurones in the spinal cord

Question 29

What are the three principal ascending tracts and their functions?

Answer 29

The principal ascending tracts are the:

1. Dorsal columns (fasciculus gracilis and fasciculus cuneatus), which carry fine touch and proprioception, 2. Spinothalamic tracts, which carry pain, temperature, coarse touch and pressure
2. Spinocerebellar tracts , which carry information from muscle and joint receptors to the cerebellum.

Question 30

What is a key descending tract and its function?

Answer 30

Lateral corticospinal tract , which controls skilled voluntary movements.

Question 31

What structure separates the cerebral hemispheres?

Answer 31

The great longitudinal fissure is a deep cleft that separates the two hemispheres. The fissure is occupied by the falx cerebri and in its depths lies the corpus callosum, containing commissural nerve fibres that run between corresponding regions of the two hemispheres.

Question 32

What is the purpose of the brainstem and how does it relate to the cerebellum?

Answer 32

The brainstem is the origin of 10 of the 12 pairs of cranial nerves (III–XII). Dorsal to the brainstem is located the cerebellum. The tentorium cerebelli lies between the cerebellum and the posterior part of the cerebral hemispheres (occipital lobes).

Question 33

What does the brainstem consist of?

Answer 33

The brainstem consists of the medulla oblongata, pons and midbrain. Through it pass all of the ascending and descending nerve fibre tracts linking the brain and spinal cord. These tracts carry sensory information from, and control the movement of, the trunk and limbs. The brainstem also contains the sites of origin and termination of most of the cranial nerves, through which the brain innervates the head. Here lie centres that control the vital functions of breathing, the circulation of blood and the level of consciousness.

Question 34

How is the cerebellum attached to the brainstem?

Answer 34

The cerebellum is attached to the brainstem by a large mass of nerve fibres that lie lateral to the fourth ventricle on either side. The mass is split nominally into three parts: the inferior, middle and superior cerebellar peduncles. These carry nerve fibres between the medulla, pons and midbrain, respectively, and the cerebellum.

Question 35

What does the cerebellum consist of?

Answer 35

An outer layer of grey matter, the cerebellar cortex, surrounding a central core of white matter. Cortical surface is highly convoluted forming a pattern of narrow folds known as folia. White matter consists of nerve fibres running to and from the cerebellar cortex and its ramifications reach towards the surface. The cerebellum is concerned with the coordination of movement and it operates at an entirely unconscious level.

Question 36

Describe the midbrain

Answer 36

Rostral to the pons is located the relatively small midbrain. On its dorsal surface can be seen the rounded eminences of the superior and inferior colliculi, beneath which runs the cerebral aqueduct.

Question 37

How are the sides of the diencaphalon separated and what does it consist of?

Answer 37

The two sides of the diencephalon are separated by the lumen of the third ventricle, of which they constitute the lateral walls. The diencephalon consists of four main divisions: in a dorsoventral direction, these are the epithalamus , thalamus , subthalamus and hypothalamus.

Question 38

Describe the epithalamus, thalamus, subthalamus and hypothalamus

Answer 38

The epithalamus is small and its most notable component is the pineal gland , which lies in the midline, immediately rostral to the superior colliculi of the midbrain.

The thalamus is by far the largest part of the diencephalon and it forms much of the lateral wall of the third ventricle. Plays an important part in sensory, motor and cognitive functions and it has extensive reciprocal connections with the cerebral cortex.

The subthalamus is a small region lying deep to the ventricular wall. It contains the subthalamic nucleus , which is closely related functionally to the basal ganglia.

The hypothalamus forms the lower part of the walls, and the floor, of the third ventricle. It is a complex and highly important region because of its involvement in the autonomic nervous system, the limbic system and the neuroendocrine system. From the ventral aspect of the hypothalamus in the midline arises the infundibulum or pituitary stalk, to which is attached the pituitary gland .

Question 39

What is the basal ganglia?

Answer 39

Several masses of cell bodies buried within the subcortical white matter.

Question 40

What lies within the great longitudinal fissure?

Answer 40

The corpus callosum, a large sheet of transversely running nerve fibres (commissural fibres) that link corresponding areas of the two cerebral cortices.

Question 41

Why is the cerebral cortex surface so convoluted?

Answer 41

Maximises the cortical surface area. Convolutions are called gyri and the furrows between them are sulci. Central sulcus separates the frontal and parietal lobes. Parieto-occipital sulcus separates P and O lobes. Lateral fissure separates frontal and temporal lobes as well as other superior lobes. Cingulate sulcus separates limbic lobe from other lobes.

Question 42

Describe the boundaries of the frontal lobe

Answer 42

Most anterior part of the cerebral hemisphere is called the frontal lobe , the most anterior convexity of which is the frontal pole. The posterior boundary of the frontal lobe is the central sulcus , which sometimes occurs as a single, continuous furrow running over the entire lateral surface of the hemisphere from the great longitudinal fissure to the lateral fissure.

Question 43

What is the limbic lobe?

Answer 43

On the medial aspect of the cerebral hemisphere, the Cingulate sulcus runs parallel to the upper margin of the corpus callosum. This delineates a region of cortex that, together with parts of the medial aspect of the temporal cortex, is sometimes referred to as the limbic lobe.

Question 44

What is an important functional area in the frontal lobe and what is it demarcated by?

Answer 44

The gyrus immediately in front of the central sulcus is referred to anatomically as the precentral gyrus . Functionally, this comprises the primary motor cortex , which is the highest level in the brain for the control of voluntary movement. Opposite half of the body is represented in each hemisphere because the neurones situated here that control movement have axons that cross over (decussate) to the opposite side of the brainstem and spinal cord, to control the motor neurones located there. Somatotopic arrangement.

Question 45

What is an important functional area in the parietal lobe and what is it demarcated by?

Answer 45

Facing the primary motor cortex across the central sulcus, lies the postcentral gyrus or primary somatosensory cortex. This is the site of termination of pathways carrying the modalities of touch, pressure, pain and temperature from the opposite half of the body and it is the region where they are consciously perceived. Opposite side perceived as ascending pathways cross over at some point during their course. Somatotopic representation.

Question 46

What is an important functional area in the occipital lobe and what is it demarcated by?

Answer 46

Primary visual cortex. It is mostly situated on the medial aspect of the hemisphere, in the gyri immediately above and below the horizontally orientated calcarine sulcus .

Question 47

What is an important functional area in the temporal lobe and what is it demarcated by?

Answer 47

Primary auditory cortex. It is localised to the superior temporal gyrus, which lies beneath, and parallel to, the lateral fissure.

Question 48

What does the limbic lobe consist of and what is it concerned with?

Answer 48

Primarily of the cingulate gyrus , lying on the medial aspect of the hemisphere parallel to the corpus callosum, and the hippocampal formation and amygdala which lie within the temporal lobe. These complex structures are concerned with the emotional aspects of behaviour and with memory.

Question 49

What is the corona radiata?

Answer 49

Cortical afferent and efferent fibres that pass between the cerebral cortex and subcortical structures, such as the basal ganglia, thalamus, brainstem and spinal cord, are arranged in a characteristic radiating pattern, the corona radiata, which reaches out to the convolutions of the cortical surface. Deeper inside the hemisphere, the fibres are concentrated into a dense sheet of white matter, known as the internal capsule.

Question 50

What are the masses of grey matter which lie lateral and medial to the internal capsule?

Answer 50

Basal ganglia constituting caudate nucleus, the putamen (together known as striatum) and globus pallidus. Caudate nucleus lies in the wall of the lateral ventricle throughout its extent and is C-shaped. The basal ganglia are principally concerned with the control of movement, posture and muscle tone

Question 51

What are the special senses coordinated by?

Answer 51

The special senses are all carried in cranial nerves and are comprised of olfaction (cranial nerve I), vision (II), taste (VII and IX) and hearing and vestibular function (VIII).

Question 52

What are the general senses and what are they coordinated by?

Answer 52

The general senses include the modalities of touch, pressure, pain and temperature (relayed from exteroceptors in the skin and interoceptors in the viscera), and awareness of posture and movement (from proprioceptors in joints, tendons and muscles). General sensory information from the trunk and limbs is carried in spinal nerves; from the head, it is carried in the trigeminal nerve (cranial nerve V).

Question 53

What is a commonality in neural pathway for general senses?

Answer 53

There is a sequence of three neurones between the sensory receptor located in the periphery and the perception of sensation at the level of the cerebral cortex

Question 54

Describe pathway of the first order neurone in a general senses pathway?

Answer 54

The first neurone enters the spinal cord through a spinal nerve, or the brainstem through the trigeminal nerve, on the same side of the body as its peripheral receptor is located. The cell body of the first-order neurone is located outside the CNS, either in the dorsal root ganglion of a spinal nerve, or in the trigeminal ganglion. Within the CNS, the axon of the first-order neurone remains on the same side (ipsilateral) and synapses upon the second neurone

Question 55

Describe pathway of the second order neurone in a general senses pathway?

Answer 55

The second-order neurone has its cell body in the spinal cord or brainstem, the exact location depending on the modality concerned. Its axon crosses over (decussates) to the other side of the CNS and ascends to the thalamus, where it terminates.

Question 56

Describe pathway of the third order neurone in a general senses pathway?

Answer 56

The third neurone in the sequence has its cell body in the thalamus and its axon projects to the somatosensory cortex, located in the postcentral gyrus of the parietal lobe of the cerebral hemisphere.

Question 57

What forms the spinothalamic tract?

Answer 57

Primary spinal afferents carrying coarse touch/ pressure, pain and temperature information from the limbs and trunk terminate near their level of entry into the spinal cord. They synapse with second-order neurones, the axons of which decussate within a few segments and thereafter form the spinothalamic tract .

Question 58

What forms the dorsal columns and where does this tract terminate?

Answer 58

Primary spinal afferents carrying proprioceptive information and discriminative (fine) touch ascend uninterrupted on the same side of the cord as their entry, forming the dorsal columns (fasciculus gracilis and fasciculus cuneatus). They terminate in the dorsal column nuclei (nuclei gracilis and cuneatus) located in the medulla. From here, second-order neurones decussate and ascend to the thalamus as a fibre tract known as the medial lemniscus.

Question 59

What forms the trigeminothalamic tract and where does this tract terminate?

Answer 59

Primary afferent neurones that enter the brainstem in the trigeminal nerve terminate ipsilaterally in the trigeminal sensory nucleus , one of the cranial nerve nuclei. From here, second-order neurones decussate and ascend to the thalamus as the trigeminothalamic tract.

Question 60

What are lower motor neurones?

Answer 60

The motor neurones that directly innervate skeletal muscle have cell bodies lying in the grey matter of the spinal cord and brainstem. They constitute the so-called ‘final common pathway’ by which the nervous system controls movement.

Question 61

What are upper motor neurones?

Answer 61

The neurones that control the activity of lower motor neurones. These form a number of descending tracts that run through the brainstem and spinal cord. Among the most important of these are the corticospinal and corticobulbar (or corticonuclear) tracts which originate partly from neurones in the motor area of the cerebral cortex.

Question 62

What part of the brain controls actions of muscle on one side of the body and what are the tracts responsible for?

Answer 62

The descending axons -> internal capsule -> brainstem, and then decussate to the other side. Hence movements of one side of the body are controlled by the opposite cerebral cortex.

Corticobulbar, or corticonuclear, fibres control the activity of motor neurones located in cranial nerve nuclei of the brainstem, which innervate skeletal muscles of the head and neck through the cranial nerves. Corticospinal fibres control the activity of motor neurones in the spinal cord, which innervate trunk and limb muscles.

Question 63

Why is the corticospinal tract also known as the pyramidal tract?

Answer 63

Descending corticospinal fibres form a prominent ridge on the ventral surface of the medulla. This is called the pyramid and, hence, the corticospinal tract is also known as the pyramidal tract . The place where these fibres cross over to the other side is called the decussation of the pyramids.

Question 64

What is the extrapyramidal system?

Answer 64

Numerous brain structures, apart from the corticospinal, or pyramidal, system are involved in the control of movement, posture and muscle tone. their descending projections as extrapyramidal pathways. Included in this definition are certain nuclei in the brainstem, such as the vestibular nuclei, the reticular nuclei ( reticular formation), the red nucleus, and also the basal ganglia plusrelated subcortical nuclei located in the forebrain.

Question 65

Why is the cerebellum important?

Answer 65

The cerebellum is an important centre in which programmes of movement, generated in the motor region of the cerebral cortex, are compared with sensory feedback concerning the speed and direction of active movements of the limbs, head and neck in space. This is essential for accurate, coordinated, purposeful movement. The cerebellum receives afferent connections from the spinal cord via the spinocerebellar tracts.

Question 66

What are the efferent and afferent connections of the cerebellum?

Answer 66

Efferent connections to the cerebellum are primarily in the form of feedback to the motor cortex via the thalamus. Efferent cerebellar projections are directed to the contralateral thalamus and cerebral cortex through a decussation in the midbrain so each side controls movement of ipsilateral side of body. Afferents to each side of the cerebellum come from the ipsilateral half of the spinal cord and brainstem and from the contralateral cerebral cortex.