Lab 9: Neurology- Histology, Brain Anatomy, & Radiology

Figure 1. Anatomy of the human brain in the context of cranial nerves

1. Cerebrum

2. Pons

3. Medulla

4. Cerebellum

5. Spinal Cord

Figure 2. Midsagittal section of the brain illustrating the diencephalon and brain stem

1. Thalamus

2. Occipital lobe

3. Pineal gland

4. 4th Ventricle

5. Cerebellum

6. Spinal cord

7. Parietal Lobe

8. Corpus callosum

9. Septum pellucidum

10. Frontal lobe

11. Hypothalamus

12. Optic chiasm

13. Pituitary gland

14. Pons

15. Medulla oblonganta

Cerebrum 

• The cerebrum is the largest region of the brain and is divided into right and left cerebral hemispheres by the deep groove called the longitudinal fissure 

• Although largely symmetrical in structure, the two hemispheres are not entirely equal in function 

• Instead, there is lateralization (specialization) of some cortical functions

• The hemispheres are covered with a folded cerebral cortex of gray matter where neurons are not myelinated (Figure 3a and 3b) 

• A fold in the cerebral is called gyrus and a shallow groove is called a sulcus

• The cerebral hemispheres are connected by a white matter called the corpus callosum

Cerebrum 2

• Gray matter of the cerebral cortex forms the outer convoluted surface of the cerebral hemispheres and the foliated surface of the cerebellum

• White matter lies deep to the cerebral and cerebellar cortices

• Cortical gray matter is made of multipolar neuron cell bodies and attendant dendrites

• Deep to the gray matter, the bordering white matter is composed of tracts of myelinated axons that project from the overlaying gray matter

• The tracts can connect one cortical region to another, to brain nuclei, and to motor neurons of the spinal cord

• Many of the multipolar neurons of the cortex are classified as pyramidal cells due to the pyramid or triangular shape of their cell bodies

Cerebrum 3

• The cerebral cortex can be divided into five basic layers

1. The molecular layer contains mainly dendrites synapsing with cortical neuron axons

2. The outer granular layer is mostly made up of stellate cells, axons, and dendrites

3. The outer pyramidal cell layer is mostly made up of pyramidal cells that increase in size as you move deeper into the layer

4. The inner granular layer is mostly made of densely packed stellate cells

5. The inner pyramidal and polymorphic layer is mostly composed of larger pyramidal cells in the more superficial portion of the layer and a wide variety of cell morphologies in the deepest parts of the layer

Figure 3a. Cerebral cortex

1. Meninges

2. Molecular layer 

3. Outer granular layer 

4. Pyramidal cells

5. Gray matter

6. Inner granular layer 

7. Inner pyramidal cells 

8. Polymorphic cells 

9. White matter 

Figure 3b. Cerebral cortex

4. Pyramidal cells 

Diencephalon

• The diencephalon consists of three paired structures: the thalamus, hypothalamus, and epithalamus 

• These gray matter areas enclose the third ventricle 

• The thalamus is a relay station for incoming information, such as sensory information or integration information, destined for higher brain areas such as the cerebral cortex 

• The hypothalamus is the autonomic control center, center for emotional response, body temperature regulation, regulation of food intake, regulation of water balance and thirst, regulation of sleep-wake cycles, and control of endocrine system functioning

• Mammillary bodies are relay stations in the olfactory pathways 

• The infundibulum is a stalk of hypothalamic tissue that connects to the pituitary gland 

• The epithalamus contains the pineal gland that secretes the hormone melatonin that helps regulate the sleep-wake cycle 

Diencephalon 2

• The pineal gland (or pineal body) is located in the epithalamus which is the superior-most part of the diencephalon 

• The pineal gland is under the control of a complex feedback loop with the suprachiasmatic nucleus (SCN) of the hypothalamus

• The pineal gland secretes the hormone melatonin (an indoleamine derived from tryptophan) that regulates circadian rhythms

FIgure 4. Pineal gland

1. Neuroglial cells 

2. Pinealocytes 

Cerebellum

• Located dorsal to the pons and medulla oblongata (Figure 5a and 5b)

• The cerebellum is primarily involved in the coordination of somatic motor function, primarily skeletal muscle contractions 

• Learned muscle patterns, such as those used to play a piano, are stored and processed in the cerebellum 

• The cerebellum functions in coordination of complex movements (i.e., walking, piano playing, and shooting a basketball)

• Like the cerebrum, it too is partitioned into cortical layers (gray matter and white matter)

• The gray matter is further divided into three layers. The most superficial layer is the molecular layer composed largely on unmyelinated fibers and scattered basket cells & stellate cells. The intermediate layer is laden with Purkinje cells followed by the deepest layer that is rich in granule cells and is therefore called the granular layer

Figure 5a. Cerebellum

1. Molecular layer

2. Purkinje layer

3. Granular layer 

4. Purkinje cell 

Figure 5b. Cerebellum

1. Molecular layer

2. Purkinje layer

3. Granular layer 

4. Purkinje cell 

Brain Stem

• The medulla oblongata, pons, and midbrain are collectively called the brain stem

• The midbrain is located between the diencephalon and the pons. This region of the midbrain is associated with inhibiting inappropriate muscle movements and dopamine signals here to ease that inhibition to allow for smooth muscle movements

• The pons is located between the midbrain and medulla oblongata and is chiefly composed of conduction tracts between higher brain centers and the spinal cord or between the motor cortex and cerebellum

• The medulla oblongata is the most inferior part of the brain stem. The medulla oblongata has some control over the cardiovascular and respiratory systems 

Brain Stem 2

• Along with the brain, the spinal cord is part of the central nervous system and has its own organization of gray and white matter 

• The anterior median fissure marks the dividing line between the mirrored right and left halves of the spinal cord

• Gray matter occupies a butterfly-shaped region that is bilaterally symmetrical about the median fissure

• The white matter surrounding the gray matter is composed of axonal tracts that propagate both afferent and efferent impulses, and from neurons on one side of the spinal cord to neurons on the other side (contralateral) and same side (ipsilateral), as well as axons that project into the ventral nerve roots 

Figure 6. Illustration of the organization of the spinal cord

1. Central canal 

2. Dorsal root

3. Dorsal horn of gray matter 

4. Lateral horn of gray matter 

5. Ventral horn of gray matter 

6. Ventral root 

7. Dorsal median sulcus 

8. Dorsal funiculus of white matter 

9. Anterior commissure 

10. Dorsal root ganglion 

11. Lateral funiculus of white matter 

12. Spinal nerve 

13. Ventral funiculus of white matter 

14. Ventral median fissure 

Cranial nerves

Say say mo mo me mo me, say me me mo mo

• Anytime we have an answer on a quiz that involves a cranial nerve, we must have the name, number, and composition 

Cranial nerves: Olfactory Nerve I- Sensory (say)

These are tiny sensory nerves of smell, which run from the nasal mucosa to the olfactory bulbs. Be careful not to confuse these with the thick olfactory bulbs and tracts of the brain

Cranial nerves: Optic Nerve II- Sensory (say)

Since this sensory nerve of vision develops as an outgrowth of the brain, it is really a brain tract

Cranial nerves: Oculomotor Nerve III- Motor (mo)

This nerve’s name means “eye mover” because it supplies four of the six extrinsic muscles that move the eye in the orbit. These muscles are the inferior oblique, medial rectus, inferior rectus, and superior rectus. 

Cranial nerves: Trochlear Nerve IV- Motor (mo)

This nerve’s name means “pulley” and it innervates the superior oblique, and extrinsic eye muscle that loops through a pulley-shaped ligament in the orbit, termed the trochlea 

Cranial nerves: Trigeminal Nerve V- Both (me)

Three branches spring from this, the largest of the cranial nerves. It supplies sensory fibers to the face and motor fibers to the chewing muscles 

Cranial nerve: Abducens Nerve VI- Motor (mo)

This nerve controls the lateral rectus 

Cranial nerve: Facial nerve VII- Both (me)

A large nerve that innervates muscles of fascial expression (among other things) 

Cranial nerve: Vestibulocochlear VIII- Sensory (say)

This is a sensory nerve for hearing and balance 

Cranial nerve: Glossopharyngeal Nerve IX- Both (me)

This nerve’s name means “tongue and pharynx,” revealing the structures it innervates. It is primarily sensory to the throat 

Cranial nerve: Vagus Nerve X- Both (me)

This nerve is the only cranial nerve to extend beyond the head and neck to supply motor and sensory fibers to the visceral body organs of the thorax and abdomen

Cranial nerve: Spinal Accessory Nerve XI- Motor (mo)

This nerve is primarily motor and supplies the trapezius and sternocleidomastoid muscles

Cranial nerve: Hypoglossal Nerve XII- Motor (mo)

This nerve’s name means “under the tongue” and runs inferior to the tongue and innervates muscles of the tongue 

PNS Histology

Figure 8. Meissner’s corpuscle

Meissner’s corpuscle function as light pressure receptors of the dermis and are located within the dermal papillae just below the epidermal/dermal border. In this picture, a Meissner’s corpuscle is encircled. 

PNS Histology

Axons branch to motor nerve endings (neuromuscular junctions) between axons of motor neurons and skeletal muscle fibers. Neuromuscular junctions (i.e., synapses) provide targeted release of the excitatory neurotransmitter acetylcholine to the sarcolemma (the motor endplate). The motor endplate is enriched with acetylcholine gated ion channels

Figure 9a. Motor nerve endings

1. Nerve fiber

2. Neuromuscular junction

Figure 9b. Motor nerve endings

1. Nerve fiber

2. Neuromuscular junction

Figure 9c. Motor nerve endings illustration

1. Synaptic vesicle

2. Acetylcholine

3. Motor endplate

4. Acetylcholine gated channel 

5. Voltage gated Ca++ channel 

6. Axon terminal 

7. Synaptic cleft 

PNS Histology 2

Peripheral nerves often provide two-way communication (efferent and afferent) containing large numbers of bundled axons. Axons are bundles together by connective tissue with an organization reminiscent of the way striated muscle is bundled together. An epineurium (not shown) surrounds the nerve. Within the epineurium-bound region, axon clusters are bound into fascicles by perineurium. Each individual axon within a fascicle is ensheathed by endoneurium 

Figure 10. Peripheral nerve, cross section

1. Endoneurium

2. Perineurium

3. Axon

PNS Histology 3

Myelin sheaths encase axons. Myelin sheaths of the PNS are derived from glial cells called Schwann cells. Schwann cell myelination serves to insulate axons from one another. Additionally, nodes of Ranvier (unmyelinated gaps between Schwann cells) allow action potentials to jump from node to node. Saltatory (“jumping’) conduction increases action potential velocity 

Figure 11. Peripheral nerve, longitudinal section

1. Node of Ranvier 

CNS Radiology

Figure 12. MRI of upper brain, transverse section 

1. Frontal horn of lateral ventricle 

2. Third ventricle 

3. Occipital horn of lateral ventricle 

4. Longitudinal cerebral fissure 

CNS Radiology

Figure 13. MRI of brain, sagittal section 

1. Corpus callosum 

2. Pituitary gland 

3. Cerebellum 

4. Fourth ventricle 

5. Pons 

6. Medulla oblongata 

7. Sphenoid sinus 

CNS Radiology

The arachnoid mater is the middle of the three meninges covering the brain and spinal cord. The dura mater is the outer meninge and the pia mater meninge is found clinging to the brain and spinal cord. The subarachnoid space is the area between the arachnoid and pia maters. The subarachnoid space is filled with cerebrospinal fluid and houses blood vessels that supply the brain 

Figure 14. MRI of cervical spine, sagittal section

1. Spinal cord

2. Subarachnoid space