Anatomy of the Nervous System

• Lecture 2 covers the Anatomy of the Nervous System
• E. Ilgın Hoşgelen-Bilgin, PhD, presented the lecture

Learning Objectives

• Apply anatomical terms related to the nervous system
• Compare the locations and functions of the meninges and ventricular system
• Identify the locations and functions of the telencephalon, diencephalon, and mesencephalon structures
• Contrast the locations and functions of the metencephalon and myelencephalon structures
• Outline the structure and functions of the spinal cord
• Identify the functions of the cranial nerves
• Differentiate between afferent and efferent axons in the spinal nerves
• Compare sympathetic and parasympathetic divisions within the autonomic nervous system

Anatomical Directions

• Anatomical directions cover the relative positions of body parts

• Terms describe location when referring to the nervous system

• Vertebrate anatomical terms include:

• Ventral: towards the stomach

• Dorsal: towards the back

• Anterior: towards the front end

• Posterior: towards the back end

• Lateral: towards the side

• Medial: towards the midline

• In humans, the longitudinal axis flexes in the brainstem at 110 degrees

• The longitudinal axis flexure means that positional terms have different meanings when applied above and below the flexure

• Proximal refers to being located close or approximate to the origin or attachment point

• Distal refers to being located far away from the origin or attachment point

• Ipsilateral refers to being on the same side of the body

• Contralateral refers to being on the opposite side of the body

• The coronal plane shows brain structures as seen from the front

• The sagittal plane shows brain structures as seen from the side

• The horizontal plane shows brain structures as seen from above

Divisions of the Nervous System

• The nervous system has two major subsystems: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)

• The CNS includes the brain and spinal cord and is encased by bone

• The PNS includes cranial nerves, spinal nerves, and peripheral ganglia

• The brain is encased in the cranium, while the spinal cord is encased in the vertebral column

• The retina is considered part of the brain, forming from the diencephalon during embryonic development

• The PNS contains separate systems for the inner and outer environments

• The PNS parts include:

• Somatic nervous system deals with the external world & allows voluntary control of body movement via skeletal muscles

• The autonomic nervous system deals with the internal world and involves involuntary physiologic processes

• Autonomic nervous system divisions:

• Sympathetic NS activates the fight-flight-freeze response

• Parasympathetic NS slows down the body for the rest and digest state

The Brain

• The brain is comprised of neurons, glia, and other supporting cells
• Brain floats in a pool of cerebrospinal fluid (CSF) and shielded behind the blood-brain barrier
• Brain weighs approximately 1.400 g and always needs roughly 20% of the body's blood
• Brain features a jelly-like structure containing two symmetrical but unidentical hemispheres
• The two hemispheres communicate through the corpus callosum

Meninges

• Meninges protect the fragile jelly-like tissue of the brain and spinal cord

• Meninges form three layers: dura mater, arachnoid membrane, and Pia mater

• Characteristics of the layers:

• Dura Mater - Tough and flexible outermost layer

• Arachnoid Membrane- Middle layer of the meninges

• Pia Mater - Innermost layer adhering to the brain's surface

• The subarachnoid space is the area between the arachnoid membrane and pia mater that is filled with CSF

• CSF fills the ventricular system and subarachnoid space and resembles blood plasma

Cerebrospinal Fluid

• Ventricles in the brain are a set of holes or cavities filled with CSF

• Cerebrospinal fluid cavity spaces also exist in the brain and spinal cord

• Ventricles include:

• Lateral

• Third

• Cerebral Aqueduct

• Fourth Ventricles

• CSF Functions:

• Support

• Shock absorption

• Homeostasis through molecular balance

• Nutrition

• Waste removal

• Immune function

• The choroid plexus produces CSF

• Excessive amounts of CSF can lead to hydrocephalus

• Neurological damage avoided by CSF balance with shunts

• Excess CSF amout leads to increase head size, balance issues, headaches, and intellectual & learning difficulties

Peripheral Nervous System

• The PNS is comprised of the Somatic Nervous System and the Autonomic Nervous System
• Cranial nerves and spinal nerves attach respectively to the brain and spinal cord
• Ganglia clusters of nerve cell bodies are found throughout the body

The Spinal Cord

• The spinal cord is located inside the spinal column, and it communicates with sense organs and muscles below the head

• The cell bodies of sensory neurons form groups clustered outside of the spinal cord

• The Bell-Magendie Law: entering dorsal roots carry sensory information to brain; ventral roots carry motor information to muscles

• Spinal Cord Details:

• Spinal nerve: A peripheral nerve attached to the spinal cord

• Afferent Axon: Carries sensory information to central nervous system

• Efferent Axon: Carries motor commands away from the central nervous system

• Dorsal root Ganglion: Contains cell bodies of afferent spinal nerve neurons

• Somatic Nervous System: Composed of nerves conveying sensory information to the CNS and transmit motor movement away to other body parts

• Autonomic Nervous System: Sends/Receives messages that regulate automatic behaviors (heart rate, blood pressure, respiration, and digestion).

• Automatic Nervous System has two divisions

• The Sympathetic Nervous System expends energy by activating systems for fight-flight-freeze responses

• The Parasympathetic Nervous System conserves energy during the rest and digest period) .

• The sympathetic nervous system sends messages to prepare the organs for activity

• Increases heart rate, blood pressure, and respiration

• Comprised of ganglia on the left and right sides of the spinal cord

• Utilizes norepinephrine as a neurotransmitter

• The parasympathetic nervous system facilitates vegetative, nonemergency responses

• Decreases the functions enhanced by the sympathetic nervous system

• Contains long preganglion axons from spinal cord & shorter postganglionic fibers that connect to the organs/muscles

• Predominantly active in relaxed states

• Releases acetylocholine as a neurotransmitter

Central Nervous System

• Consists of the brain and spinal cord
• During development, the central nervous system starts as a hollow tube that thickens into its final form
• There are three main divisions of the brain: hindbrain, midbrain, and forebrain

Hindbrain

• The hindbrain includes the medulla, pons, and cerebellum and sits at the posterior area of the brain
• The medullary respiratory center drives heart rate, breathing, vomiting, salivation, and coughing
• The raphe nucleus is in the medulla and pons controls sleep and dreaming using serotonin
• Many neurons from the "somatic system" pass through the pons
• In hindbrain, cerebellar folds are involved in movement control, coordination, and posture

Pons

• Pons are present on each side of the medulla, ventrally and anteriorly and contain part of the reticular formation and raphe system

• The pons also works to increase arousal and readiness of other parts of the brain

• Reticular formation descending portion controls motor parts of the spinal cord

• Reticular formation ascending portion delivers output to the cerebral cortex, increasing arousal and focusing attention

• The pontine reticular activating system leads to several functions:

  • Wakefulness - Ability to awaken upon hearing an alarm
  • Filtering Sensory Information - Focus ability due to background noises
  • Emotion and motivation- Alertness from good news

• Damage to the RAS can lead to drowsiness or even a coma

Cerebellum

• The cerebellum regulates motor movement, balance, and coordination
• The cerebellum shifts attention between auditory and visual stimuli
• The cerebellum is involved with motor output and learning skills and is responsible in voluntary motor skills

Midbrain

• The midbrain, also known as the mesencephalon, is made of the tectum and tegmentum

• Midbrain structures:

• Tectum - the "roof"

• Tagmentum- intermediate level, has cranial nerve nuclei and part of the reticular formation

• Superior & inferior colliculus- on each tectum side receive and process sensory information

• The Darkly stained region of tegmentum facilitates movement

• Substantia nigra communicates with the caudate nucleus and putamen in basal ganglia, giving rise to the dopamine-containing pathway that is needed in movement

Forebrain

• The forebrain, comprised of the telencephalon and diencephalon, constitutes the most anterior and prominent part of the mammalian brain

  • Outer cortex
  • Regions underneath cortex

• Each side processes sensation and controls motor activity for the opposite body side

• Gage, kind before accident, after was disrespectful, abusive, harsh, but retained memories

• Forebrain contains:

• Cerebral cortex, which has grey matter layers and subcortical structures

Thalamus

• It directs sensory signals to the correct areas of the cerebral cortex and acts as a gateway to the cerebral cortex
• It receives sensory, motor, and prioritizes signals
• Helps regulate consciousness
• Connects with limbic structures involved in memories, emotion, and arousal

Limbic System

• The limbic system consists of many interlinked structures around the brainstem
• The limbic system includes the olfactory bulb, hypothalamus, hippocampus, amygdala, and cingulate gyrus of the cerebral cortex
• Limbic system is associated with motivation, emotion, drive, and aggression

Hypothalamus

• Hypothalamus is is an area at the brain's base
• Leads to pituitary gland to alter the release of hormones
• In charge of behaviors like eating, drinking, sexual activity and motivated behaviors
• Thalamus and hypothalamus collectively make the "diencephalon."

Pituitary Gland

• Pituitary gland is a hormone-producing gland found at the hypothalamus base
• It secretes hormones that regulate other hormone-secreting glands

Basal Ganglia

• The Basal Ganglia comprises the caudate nucleus, putamen, and globus pallidus

• Primarily associated with planning and learning motor movements

• Partakes in multiple aspects of emotional expression and memory

• Basal forebrain comprised of structures that lie on dorsal side of the forebrain includes:

• Nucleus basalis (basal ganglia) that gets input hypothalamus/basal ganglia, releases acetylcholine, vital for arousal, wakefulness and attention

• Other Forebrain parts:

• Central canal: Fluid-filled channel at the spinal cord's center

• Ventricles cavities that contain fluid

• Cerebrospinal fluid is clear that:

• Cushions

• Stores hormones and nutrients

• Meninges are membranes surrounding spinal cord and brain

Cerebral Cortex

• Mammalian brain's most notable component contains cellular layers on the surface of the cerebral hemispheres where:

  • Is divided into two halves
  • Contains corpus callosum that holds the two halves together
  • More highly developed in humans than compared to others

• The cerebral cortex structure has six layers, or laminae, that are distinct (cells in it are all parallel)

• Cortex cells arranged into columns that lie perpendicular to laminae

• Cerebral cortex is divided into types by structure: occipital, central sulcus, post central gyrus, primary somatosensory

• Primary brain functions:

• Frontal lobe that is needed for movement planning

• Body emotions and recent memory

• Occipital lobe for vision

• Temporal lobe for hearing and advanced visual processing

• Occipital lobe (at the back of the cortex region):

• Striate cortex / visual cortex that is highly related to visual input

• Damage to the area leads to blindness.

• Parietal lobe details:

• Touch sensations, body sensations, muscle stretch receptors, and information joints

• Processes integratively regarding eye, heads and body positions from informations joints and muscles

• Temporal lobe(located on sides of each hemisphere) related to temples

• Processing auditive data

• Processing language/speaking comprehension

• Responsible movements of vision, emotional or motive behaviors

• Damage may lead to loss of speaking capacity/recognition or emotional intelligence

• Frontal lobe important for:

• Integration

• Sensory control for whole body

• Thinking/planning

• Prefrontal cortex functions:

• Higher-order functions (planning, abstract thinking).

• Remembering long range events and information (working memory)

• Regulations to impulsive behaviors and managing more complicated situations/behaviors.

Various cerebral cortex parts do not perform alone or separately. All regions interconnect, no single part has total power over the others

The binding problem

• The binding problem references how auditory/other regions form perceptions from items