7.8 - Introduction to Neuroanatomy

Question 1

What are the three ways the brain can be examined?

Answer 1

• sagittal section - divides brain into two separate halves down centre
• horizontal / frontal section - brain spliced perpendicular to long axis of body
• coronal / frontal section - brain slices parallel to long axis

Question 2

When looking at the brain what do the terms medial and lateral mean?

Answer 2

• medial - closer to middle of brain
• lateral - closer to sides of brain

Question 3

What is the CNS made up of?

Answer 3

• brain and spinal cord
• protected by cranium and vertebral column
• most complex part of nervous system containing majority of nerve cell bodies and synaptic connections

Question 4

What is the PNS made up of?

Answer 4

• connects CNS and structures in the periphery of the body, from which it receives sensory information and to which it sends controlling impulses
• consists of nerves joined to the brain and spinal cord (cranial and spinal nerves) and their ramifications with the body
• 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
• also contains many peripherally located nerve cell bodies, some of which are aggregated within the ganglia

Question 5

Describe the somatic and autonomic nervous systems

Answer 5

• somatic nervous system - neurones concerned with detecting changes in the external environment, or with control of movement
• autonomic nervous system - neurones that detect changes in, and control the activity of, the viscera
• autonomic nervous system is divided into two anatomically and functionally distinct parts - sympathetic (increases energy) and parasympathetic (conserves energy) divisions, which generally have opposing (antagonistic) effects

Question 6

Describe afferent neurones, efferent neurones and interneurones

Answer 6

• afferent neurones - nerve cells that carry information from peripheral receptors to the CNS - if the information they carry reaches consciousness, they are also called sensory neurones
• efferent neurones - carry information away from the CNS and if they innervate skeletal muscle to cause movement, they are also called motor neurones
• interneurones - relay neurones - located entirely within CNS

Question 7

Describe the difference between white and grey matter

Answer 7

• white matter refers to areas of the CNS that are mainly made up of myelinated neurones
• grey matter is a major component of the CNS, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses and capillaries
• cerebral cortex - highly convoluted outer mantle of grey matter
• inner core of white matter, within which are located further masses of grey matter

Question 8

What are the two cerebral hemispheres incompletely separated by?

Answer 8

• a deep cleft - the great longitudinal fissure
• the fissure is occupied by the falx cerebri and in its depths lies the corpus callosum - contains commissural nerve fibres that run between corresponding regions of the two hemispheres

Question 9

What is the basic organisation of the brain?

Answer 9

• brain conventionally divided into forebrain, midbrain and hindbrain
• hindbrain further subdivided into the medulla oblongata, pons and cerebellum - constitute the brainstem
• forebrain consists of diencephalon (thalamus and hypothalamus) and the cerebral hemisphere
• within the cerebral hemisphere lie several large nuclei called the basal ganglia
• brain possesses 12 pairs of cranial nerves carrying afferent and efferent fibres, principally to and from structures of the head
• two cerebral hemispheres linked by the commissural fibres of the corpus callosum
• surface of cerebral hemisphere consists of cortical grey matter, folded into gyri and sulci - beneath lie the dense fibre masses of the corona radiata and internal capsule; surface divided into lobes
• limbic lobe contains regions for memory and emotional aspects of behaviour

Question 10

What is the anatomy of the spinal cord?

Answer 10

• lies within the vertebral canal
• bears 31 pairs of spinal nerves through which it receives fibres from + sends fibres to the periphery
• near the cord, spinal nerves divide to form dorsal and ventral roots
• dorsal roots carry afferent fibres with cell bodies in dorsal root ganglia
• ventral roots carry efferent fibres
• consists of a central core of grey matter, containing several nerve bodies and an outer layer of white matter containing nerve fibres
• within grey matter, the dorsal horn contains sensory neurones, the ventral horn contains motor neurones and the lateral horn contains preganglionic sympathetic neurones
• within the white matter rub ascending and descending nerve fibre tracts, which link the spinal cord with the brain

Question 11

What are the meninges?

Answer 11

• the brain and SC are covered by three meningeal layers - the dura mater, arachnoid mater and pia mater
• two sheets of cranial dura mater, the falx cerebri and tentorium cerebelli, incompletely divide the cranial cavity into compartments
• the cranial dura mater contains dural venous tissues, which act as channels for the venous drainage of the brain
• beneath arachnoid mater lies the subarachnoid space in which cerebrospinal fluid (CSF) circulates
• brain supplied with blood by the internal carotid and vertebral arteries
• SC supplied with blood by vessels that arise from the vertebral arteries, reinforced by radicular arteries derived from segmental vessels

Question 12

What is the ventricular system?

Answer 12

• ventricles are a network of cavities that are distributed throughout the brain
• ventricles lined with a specialised membrane called the choroid plexus which is composed of glial cells called ependymal cells - specialised to secrete CSF which then flows through the brain via the ventricles
• main role is production and distribution of CSF

Question 13

What is the role of CSF?

Answer 13

• surrounds brain - protective layer which reduces strain forces e.g. gravity on brain
• constantly flows through and around the brain, removing toxins and regulating the extracellular environment of neurones
• blockage of CSF circulation e.g. by a tumour = increases pressure of ventricles –> expansion - causes hydrocephalus

Question 14

How many ventricles are there?

Answer 14

• four ventricles
• two C-shaped lateral ventricles (one in each cerebral hemisphere), which are connected to a third ventricle by the intraventricular foramen
• third ventricle is a narrow cavity that runs along the midline of the diencephalon
• third and fourth ventricles connected by cerebral aqueduct
• fourth ventricle wedged between cerebellum on one side + brainstem on other - shaped like a tent whose peak protrudes into cerebellum
• three openings in the fourth ventricle that allow CSF to enter subarachnoid space = CSF leaves the ventricular system via the fourth ventricle
• fourth ventricle extends to, and is continuous with, the central canal - CSF-filled cavity that runs the length of the SC