NeuroanatomyWe all know that hesitation when you’re about to open a neuroanatomy textbook. It feels as though you’re about to go to Mordor. That’s usually due to the complexity of the subject, which textbooks often fail to simplify and thus give fuel to the theory that the nervous system is so hard to learn.
It doesn’t have to be that way. In this article we will introduce you to the main concepts of neuroanatomy and the major structures of the nervous system. After that, you can dive into our series of easy-to-read study materials, so that at the end of your neuroanatomy journey you’ll feel more like Frodo Baggins, rather than the fallen Boromir.
- What is a neuron?
- Nervous system
- Central nervous system
- Peripheral nervous system
- Neural pathways and spinal cord tracts
- Video tutorials
- Related diagrams and images
What is a neuron?
A neuron (nerve cell) is the functional unit of the nervous system. They receive and transmit neural impulses. Meaning that, neurons receive, process and integrate information from all regions of the body and send instructions on how body tissues are to respond to environmental and internal events.
Neurons are comprised of a cell body (soma) and neural processes (axons and dendrites). They are structurally classified based on how many processes they have: unipolar, pseudounipolar, bipolar, and multipolar. The axons of most neurons are wrapped with a white substance called myelin. Myelinated axons are found in the white matter, giving it its colour and distinguishing it from grey matter (neuronal cell bodies).
Myelin insulates axons and allows quicker transmission of electrical impulses. A bundle of axons (nerve fibers) in the CNS is called a tract. In the PNS this bundle is called a nerve. Besides from neurons, there are other nervous system cells, for example glial cells, which play supporting roles.
Learn about the cells of the nervous system here.
The nervous system controls every aspect of body function. Ranging from essential physiological processes (body temperature and the sleep-wake cycle), voluntary commands (movement), all the way to the most complex features of a human being (higher-order thinking and the whole spectrum of emotional behaviour).
There are two structural divisions of the nervous system. The central nervous system or CNS (brain and spinal cord) and the peripheral nervous system or PNS (all neural tissue outside the CNS). Functionally, the nervous system is divided into the somatic nervous system and the autonomic nervous system. Informally described as our voluntary and involuntary systems, respectively. Information flow within the nervous system can be described as afferent or efferent. Afferent pathways carry information from peripheral tissues to the CNS (sensation), while efferent pathways carry commands on how to respond (motor).
Here’s a nervous system starter pack for you, just a few clicks away. Note that in this pack you will find a specially designed quiz to test your knowledge about the neuronatomy! Feel free to take the quiz as many times as you like, and learn more about the nervous system, its divisions, structure and functions!
Central nervous system
The central nervous system (CNS) consists of the brain and spinal cord. The brain is found in the cranial cavity, while the spinal cord is found in the vertebral column. Both are protected by three layers of meninges (dura, arachnoid, and pia mater).
The brain generates commands for target tissues and the spinal cord acts as a conduit, connecting the brain to peripheral tissues via the PNS. The brain is divided into the cerebrum, diencephalon, cerebellum, and brainstem. The spinal cord is continuous with the brainstem.
Get started with central nervous system anatomy through our comprehensive articles.
Cerebrum and cerebral cortex
The cerebrum makes up most of the brain. It is found in the cranial vault. The cerebrum consists of two cerebral hemispheres (left and right) and five lobes. All lobes (except one) are named according to the cranial bones on which they lean: frontal, parietal, temporal, occipital and insular lobes. The insular lobe is hidden just beneath the frontal, temporal, and parietal lobes. ‘Insula’ means island, which the insular lobe is indeed–an isle of gray matter hidden under the surface of the cerebrum.
You’ll probably encounter the term limbic lobe as well, but this is not an actual lobe. Rather it’s a functional group of interconnected regions of the brain which together control emotions, memory and spatial perception. The cerebrum together with the hippocampus, amygdala, olfactory bulb, and basal ganglia comprise the telencephalon.
The most superficial layer of the cerebrum is the cerebral cortex. It is a layer of grey matter which displays numerous folds (sulci and gyri), can be categorization structurally (cortical cytoarchitecture) or functionally (Brodmann areas), and is home to areas such as the primary motor cortex and the primary somatosensory cortex, both of which house a homunculus.
White matter connections extend between the cerebral cortex grey matter to other parts of the same cerebral hemisphere (projection fibers); to the opposite hemisphere (commissural fibers); and to structures outside the cortex (association fibers).
Learn more about cerebral cortex and its structure with our videos and brain anatomy quiz.
The subcortical structures are a group of diverse structures found deep within the brain. They include the diencephalon (thalamus, epithalamus, subthalamus and hypothalamus), pituitary gland, limbic structures and the basal ganglia.
These structures show a great variety of functions, for example;
- The hypothalamus and pituitary gland are involved in hormone production and regulation
- The limbic system (includes; hippocampal formation, fornix, amygdala, insular cortex, and others) is involved in memory, olfaction, emotional behaviour and overall physiological balance of the body (homeostasis)
- The basal ganglia are a functional group of nuclei which together comprise a unit of the extrapyramidal motor system, modifying motor activity
Learn more about the subcortical structures here.
The brainstem is the most caudal part of the brain. It consists of the midbrain (mesencephalon), pons and medulla oblongata. The cerebellum, pons and medulla oblongata are often grouped together under the name hindbrain (rhombencephalon). The importance of the brainstem lies in several of its features, together giving the brainstem the informal definition as our survival center:
- It contains all cranial nerve nuclei (except CN I, CNII), providing somatic and autonomic control of the head and neck.
- It contains the nuclei of the reticular formation
- It contains sympathetic and parasympathetic nuclei, providing vital centers that control activities like breathing, heart rate and vasomotion.
- All pathways between the spinal cord and the cerebrum / cerebellum pass through the brainstem.
Get to know the anatomy of the brainstem with our articles, video tutorials and quizzes.
The cerebellum lies between the cerebrum and the medulla of the brainstem. It plays an important role in regulating motor functions; participating in the planning and modulation of motor activity, including the coordination of the body while moving.
Like the cerebrum, the cerebellum has two hemispheres (left and right). They are connected by a midline mass called the vermis. It also has three lobes; anterior, posterior and flocculonodular. The cerebellar cortex forms the outermost layer of cerebellum and is comprised of grey matter. Important structures of the cerebellum include it's many paired nuclei within its deep white matter and the cerebellar peduncles.
You can learn more about cerebellum anatomy and function here.
The spinal cord is found in the vertebral column. It is continuous with the brainstem, extending from the foramen magnum of the occipital bone to the L1/L2 vertebra. This caudal part of the CNS transmits information to and from the periphery by interacting with the peripheral nervous system. However, it is more than just a channel between the brain and the body–it also modifies and integrates the information that passes through it and participates in reflexes.
The spinal cord consists of 5 segmental groups;
- Cervical spine - 8 segments (C1-C8)
- Thoracic spine - 12 segments (T1-T12)
- Lumbar spine - 5 segments (L1-L5)
- Sacral spine - 5 segments (S1-S5)
- Coccygeal spine - 1 segment (Co1)
Contrary to the brain, the spinal cord’s outermost layer is formed of white matter. This is divided into three funiculi (anterior, lateral, and posterior) containing pathways travelling between the brain and the periphery. The central mass of the spinal cord is a butterfly-shaped grey matter which contains neuronal cell bodies.
Master spinal cord anatomy with our study materials.
The meninges are the three membranous layers of dura, arachnoid and pia mater that envelope the brain and the spinal cord.
Meninges act to protect CNS structures, form partitions and provide spaces. The dural partitions separate the cerebrum and cerebellum from each other and divide their hemispheres (falx cerebri, tentorium cerebelli, falx cerebelli, diaphragma sellae). The meningeal spaces contain the dural venous sinuses and the cerebrospinal fluid filled subarachnoid cisterns.
Study the anatomy of meninges with our resources.
Ventricles and CSF
The ventricles are interconnected cavities located deep within the brain. They are filled with cerebrospinal fluid (CSF) which functions to protect the brain and spinal cord, provide nutrients and remove waste. There are the four ventricles housed within the brain:
- Two lateral ventricles - within the lobes of the cerebrum
- Third ventricle - between the thalami
- Fourth ventricle - located over the pons and medulla oblongata and underneath the cerebellum
CSF is produced by the cells of the choroid plexuses found within the walls of these ventricles. It then circulates through the ventricles via foramina located between them. From the fourth ventricle CSF accesses a system of subarachnoid cisterns, flowing through the subarachnoid space of the brain and spinal cord until it’s finally absorbed into the venous system of the CNS.
Fill your neurons with some quality knowledge about CSF and the ventricular system.
Brain blood supply
The brain's arterial supply is provided by two major sources; the internal carotid and the vertebral arteries. The internal carotid artery forms the anterior circulation of the brain, supplying the anterior and middle parts of the cerebrum. The vertebral arteries supply the posterior cerebrum, brainstem and cerebellum (posterior circulation). These two circulations anastomose at the base of the brain forming a vascular network called the circle of Willis.
We have you covered with everything you need to know about the arterial supply of the brain and spinal cord.
Venous blood from the brain is drained through a system of superficial and deep cerebral veins. Superficial cerebral veins drain the cortex, while deep veins drain deep brain structures. Both groups eventually empty into the dural venous sinuses, enlarged venous channels found within the dura mater. Venous sinuses drain into the internal jugular vein.
Want to learn more about the venous drainage of the brain? We’ve got you covered with some great articles, video tutorials and quizzes.
Peripheral nervous system
The peripheral nervous system consists of 12 pairs of cranial nerves, 31 pairs of spinal nerves, and all their branches. Spinal nerves originate from spinal cord segments and innervate the body. Cranial nerves originate from the brainstem, predominantly innervating the head and neck region. Functionally, the PNS can be divided into the somatic and autonomic (sympathetic and parasympathetic) nervous systems.
Start with peripheral system anatomy here.
Cranial nerves originate from nuclei in the brain. They emerge from foramina and fissures of the cranium to provide sensory and motor supply to the head and neck. Only the vagus nerve extends beyond the neck to innervate thoracic and abdominal viscera. Their numerical order (1-12) is determined by their skull exit location (rostral to caudal).
|Cranial nerve 1||Olfactory nerve (CN I)|
|Cranial nerve 2||Optic nerve (CN II)|
|Cranial nerve 3||Oculomotor nerve (CN III)|
|Cranial nerve 4||Trochlear nerve (CN IV)|
|Cranial nerve 5||Trigeminal nerve (CN V)|
|Cranial nerve 6||Abducens nerve (CN VI)|
|Cranial nerve 7||Facial nerve (CN VII)|
|Cranial nerve 8||Vestibulocochlear nerve (CN VIII)|
|Cranial nerve 9||Glossopharyngeal nerve (CN IX)|
|Cranial nerve 10||Vagus nerve (CN X)|
|Cranial nerve 11||(Spinal) Accessory nerve (CN XI)|
|Cranial nerve 12||Hypoglossal nerve (CN XII)|
Learn cranial nerve anatomy with articles, videos, and quizzes now at Kenhub.
Spinal nerves are the major output of the spinal cord. They arise in pairs from corresponding spinal cord segments. There are 31 pairs of spinal nerves; 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal
Spinal nerves are sort of a hybrid output for each part of the nervous system, as they are mixed nerves containing sensory, motor and autonomic fibers. They arise from two roots, anterior (motor) and posterior (sensory). The roots unite and the nerve exits from the spinal cord through the corresponding intervertebral foramen to innervate areas of the body. Spinal nerves innervate their target organs directly, or by forming neural networks called plexuses. Notable plexuses are:
- Cervical plexus (C1-C4) - innervates neck structures
- Brachial plexus (C5-T1) - innervates the upper limb
- Lumbar plexus (L1-L4) - innervates the lower abdominal wall, anterior hip and thigh
- Sacral plexus (L4-S4) - innervates the pelvis and the lower limb
Areas of skin innervated by one spinal nerve are called dermatomes. Groups of muscles innervated by one spinal nerve are called myotomes.
Learn the anatomy of spinal nerves with this set of study materials.
Neural pathways and spinal cord tracts
Neural pathways are organized bundles of axons, connecting a specific part of the gray matter with a target tissue. There are two types of pathways: ascending (afferent, sensory) or descending (efferent, motor).
Ascending pathways send information from peripheral tissues and transmit it to the CNS. The CNS interprets this information so that the brain knows what’s going on in, and around, the body. Descending pathways transmit information from the CNS to peripheral tissues. These define how the body will respond. So, if you feel that some part of your skin itches (afferent), you can respond by scratching it (efferent).
Solidify your knowledge and read more about general principles of neural pathways here.
Ascending pathways transmit sensory information from our internal and external body environment. Sensations of proprioception and fine touch are carried through the dorsal columns which, together with the medial longitudinal fasciculus, forms the dorsal column-medial lemniscus pathway (gracile and cuneate fasciculi).
Sensations of temperature, crude touch and pain travel through the anterior and lateral funiculi of the spinal cord (spinothalamic tracts, also referred to as the anterolateral sensory system). The anterolateral system also includes the spinoreticular pathway (behavioural awareness) and spinotectal (spinomesencephalic) pathway (inhibiting and controlling pain sensations).
Dive into our sensory pathways article and find out why we are so sensitive.
Descending pathways control the movements of the body. They are classified in two large groups; pyramidal and extrapyramidal. The pyramidal motor system (corticonuclear and corticospinal pathways) originates from the motor cortex to control voluntary movements of skeletal muscles.
The extrapyramidal motor system (rubrospinal, tectospinal, reticulospinal, and vestibulospinal tracts) originate from nuclei in the brainstem. By synapsing in the spinal cord this system controls other aspects of locomotor activity besides pure movement, such as coordination, reflexive movements and body posture.
Learn the anatomy of spinal cord descending tracts here.