Nervous System: Classifications & Functions

• The nervous system is organized, beginning with an overview of the components of the brain, followed by demonstrating anatomical maps and transverse sections of the brain, and the cerebral cortex

Anatomical/Structural Classification of the Nervous System

• The nervous system is classified into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)
• The Central Nervous System consists of the brain and spinal cord
• The brain consists of the Telencephalom and the Diencephalon
• The Peripheral Nervous System consists of cranial nerves and ganglia, plus spinal nerves and ganglia

Functional Classification of the Nervous System

• The nervous system can be divided into sensory and motor divisions
• Sensory division includes somatic and visceral (autonomic) components
• Motor division also has somatic and visceral (autonomic) components
• Both visceral components are further divided into sympathetic and parasympathetic systems

Overview of Functions of the Nervous System

• The nervous system detects changes via the sensory system
• It processes information in the Central Nervous System
• The nervous system then responds via the motor system
• The somatic sensory and motor nerves are linked to the external environment
• The autonomic nervous system connects to the internal environment via sensory and motor components

Somatic Motor & Sensory System

• The Sensory system includes a Sensory receptor in the head, leading to the Cranial sensory ganglion, which then leads to the Sensory Cortex and Motor Cortex via the Thalamus
• Also in the Sensory system the receptor is in the trunk and limbs, leading to the Dorsal root ganglion and then the Dorsal horn
• The Motor system includes the Lower motor neuron, which leads to Voluntary muscles in the head or in the trunk and limbs

Autonomic Motor System

• The autonomic nervous system consists of two neurons connecting the effector organs (smooth muscles/glands)
• The sympathetic system has preganglionic neurons that start in the lateral horns of the T1-L2 spinal segments
• The parasympathetic system preganglionic neurons start in the lateral horns of S2-4 or parasympathetic nuclei of CN III, CN VII, IX, and X
• The postganglionic neurons in the sympathetic system start in the sympathetic chain
• The postganglionic neurons in the parasympathetic system start in the sacral parasympathetic ganglia
• Cranial nerve parasympathetic ganglia include Ciliary (CN III), Submandibular/Pterygopalatine (CN VII), Otic (IX), and multiple plexuses (X)

Components of the Brain

• The brain consists of the Procencephalon (forebrain), Mesencephalon (midbrain), and Rhombencephalon (hindbrain)
• Procencephalon is further divided into the telencephalon and diencephalon
• Rhombencephalon is divided into the pons, medulla, and cerebellum

Brain Composition

• The brain comprises neurons, neuronal axons (white matter), and neuroglial cells
• Cell bodies of neurons make up the gray matter
• There are 3 types of white matter: association fibers, commissural fibers, and projection fibers

Brain Anatomy

• Key structures include the telencephalon, lateral ventricles, and cerebral cortex
• Also consists of basal nuclei, diencephalon (thalamus and hypothalamus), and the third ventricle
• The midbrain is connected to the aqueduct
• The brainstem consists of pons, central canal, medulla, and cerebellum
• White matter consists of commissural fibers (corpus callosum) and association fibers

Cerebral Cortex

• Lateral View: The surface of the cerebral hemispheres is convoluted with elevations (gyri) and grooves (sulci)
• The arrangement increases the surface area of the cerebral cortex within the cranial cavity
• Three main sulci divide the cerebral hemispheres into four lobes: frontal, parietal, temporal, and occipital
• The central sulcus separates the frontal and parietal lobes
• The parieto-occipital sulcus separates the parietal and occipital lobes
• The lateral sulcus separates the frontal and parietal lobes from the temporal lobe

Lobes of the Cerebral Hemispheres

• Frontal Lobe: Includes the precentral sulcus, superior frontal sulcus, and inferior frontal sulcus
  • The sulci divide the frontal lobe (lateral part) into four main gyri, which are the Precentral which is anterior, and the Superior frontal, Middle frontal and Inferior frontal gyri
• Temporal Lobe: Includes the lines depicting the Superior Temporal sulcus & Inferior Temporal sulcus
  • There are 3 gyri including the Superior, Middle and Inferior temporal gyri

Parietal Cortex

• Extends from the Central Sulcus, where the Postcentral Sulcus in located
• Also includes the Lateral Sulcus, Postcentral gyrus, Supramarginal gyrus and Angular gyrus
• Medial View: The medial view appears more complex and includes the cerebral hemisphere, diencephalon, brainstem, and cerebellar hemisphere

Cerebral Cortex Function (Medial View)

• The central sulcus is barely appears on the medial surface
• Frontal lobe sits on the anterior of the central sulcus and the parietal lobe sits on the posterior
• The Parieto-occipital sulcus can be seen clearly on the medial side, and divides the parietal and occipital lobes
• The medial part of the temporal lobe is mostly covered by the brainstem

Hierarchical Cortical Function

• Cerebral cortex is responsible for perception, information processing, decision making, and execution of planned processes
• Sensory cortical areas are responsible for perception
• Primary sensory areas are related to basic perception
• Unimodal sensory association areas involve detailed perception
• Detailed processing and decision-making occur in multimodal association areas
• Planning and execution are controlled by primary and association motor cortices

Primary Sensory Cortical Areas

• Responsible for detecting basic sensory dimensions
• Involved in the Primary general sensory cortex, for locating intensity, for texture The visual cortex where colours, edges, light and dark are processed
• Detection of basic sensory dimensions Primary auditory cortex, which responds to simple sounds, pitch, and tones.
• The Somatosensory cortex is located in the post-central gyrus, including Broadmann areas 3, 1, and 2
• The Auditory cortex is located in the superior wall of the superior temporal gyrus - Broadmann areas 41, 42
• The Visual cortex is located on either side of the Calcarine sulcus - Broadmann areas 17

Unimodal Association Sensory Areas

• Detailed perception of stimuli rather than simple contours, textures, tones, and colors processed by primary sensory cortices
• Temporal visual association area helps recognize faces, animals, vehicles, and trees
• Temporal auditory association area helps recognize specific sounds (e.g., a bird sound)
• Parietal somatosensory association area is important for stereognosis, graphaesthesia, and spatial awareness
• Somato-sensory areas are located on the Lateral view
• Auditory Association cortex is located in the Wernicke's area
• The Visual association cortex is located in the Anterior view

Motor Cortical Areas

• Located in the pre-central gyrus which include the Broadmann area 4
• Has Unimodal motor areas which are located near to the primary motor cortex
• Two areas are involevd 1)Premotor and 2)Supplementary motor area
• Also involed in movement such as preparing motor plans
• The Broca's area is also required, and is a specific association motor area for planning speech & writing
• The Frontal Eye Field located in the middle frontal gyrus is to assist with Horizontal conjugate gaze

Multimodal Association Areas

• The Posterior Multimodal association area is located in the perital lateral
• The Limbic Multimodal association area is located in the Anterior view
• The Cingulate gyrus and The orbitofrontal cortex is located in the medial division

Cortical Function Example

• Sensory inputs in a chemistry lab when accidentally dropping acid
• Higher level sensory processing at Posterior MMAA
• PFC (anterior MMAA) makes a decision and informs motor cortical areas
• See it shatter (the 1ry and unimodal association visual areas), hear it smash (the 1ry and unimodal association auditory areas) and feel the burn (the 1ry and unimodal association Somato-sensory areas as an example of cortical function

Functions – Frontal Lobe

• Planning, control, and execution of voluntary movements on the contralateral side
• Horizontal conjugate gaze to the contralateral side (Looking to RIGHT by Left Frontal eye field & vice versa)
• Planning & Execution of speech are on the Left side only (Broca's area)
• Working memory and attention are also frontal lobe functions
• Decision Making, behavioural and problem solving are all frontal lobe functions

Functions – Parietal Lobe

• Both sides of the Parietal Lobe process individual somato-sensory modalities from the contralateral side
• Integrated of multiple sensory models are done on the contra lateral side
• Spatial awareness is on the right side of the parietal lobe
• Maths Skills are found on the left side of the parietal lobe
• Finger identifications plus right and left functions are located on the left side Writing is also a lefft side parietal function

Functions – Occipital Lobe

• Processing of visual sensory inputs from the contralateral visual fields

Functions – Temporal Lobe

• Processing Auditory inputs from both ears
• Comprehension Language is in the only left side
• Both sides of this together help consolidate memory

Corpus Callosum

• Consists of commissural fibers connecting the 2 cerebral hemispheres
• The connections are seen from the top side
• And as longitudal sections
• It consists Forceps major ( posterior radiation) and Foorceps minor

Corpus Callosum – Parts

• The parts of this include the Splenium (posterior most portion connects Posterior temporal & Occipital cortices), the Body ( the middle portion and connects the Posterior frontal & Parietal), and Genu
• And the final connection that connects to the Orbitofrontal

Fornix & Hippocampus

• Fornix is a collection of axons connecting Hippocampus and the Mammillary body
• It is located inside the temporal lobe in the inferior horn of the lateral lobe
• 2 globular structures extend from the mamillary body
• This plays a memory connecting structure

Basal Nuclei

• Basal nuclei are collections of subcortical gray matter including caudate nucleus, putamen, and globus pallidus
• Globus pallidus consist of GP externa and GP interna
• Functionally linked structures for clinicians are the subsantia nigra

Basal Nuclei classifications

• The two major classification components involved is the Straiatum and the Lentiform Nucelus
• The Putamen and the Globus pallidus make up the Nucleus

Basal Nuclei: Locations & Relations

• In a Lateral View of the internal capsule there is the Brainstem within the cerebral hemisphere
• Note that most of the caudate and thalamus are covered to to their medial proximations
• On the 3D digital lateral view its obvious the connections of the lentiform
• The Infero-lateral region of the Thalmus, its possible to to view the substantia Nigra.

Diencephalon

• 2 "egg" contains 2 shaped structures in the Thalamus and Hypothalamus
• Surrounded by the cerebellum
• The medial region it is connected to and forms the midbrain
• The anterior of 3rd and caudate nucelus can be found and connected

Diencephalon – Mamillary bodies

• Can arise from the posterior structures of the hypothalamuses structure
• They are also connected to the Thalamus.