Nervous System Anatomy

Anatomy of the Nervous System

• The nervous system divides into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
• The CNS includes the brain and spinal cord. The PNS divides into the Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS).
• The ANS consists of the sympathetic and parasympathetic systems.

Anatomical Directions and Planes of Section

• Anatomical directions are essential for describing the location of structures in the body.
• The coronal plane shows brain structures as seen from the front.
• The sagittal plane displays brain structures from the side.
• The horizontal/transverse plane reveals brain structures from above.
• Dorsal refers to toward the back, away from the ventral (stomach) side.
• Ventral means toward the stomach, away from the dorsal (back) side.
• Anterior points to the front end, while posterior points to the rear end.
• Superior is above another part, and inferior is below another part.
• Lateral is toward the side, away from the midline. Medial is toward the midline, away from the side.
• Proximal is located close to the point of origin or attachment.
• Distal is located more distant from the point of origin or attachment.
• Ipsilateral refers to the same side of the body; contralateral refers to the opposite side of the body.

Protecting and Supplying the Nervous System

• The nervous system is protected by three layers: meninges, cerebrospinal fluid, and blood supply.

Meninges

• Meninges are layers of membranes covering the CNS and PNS.
• The first layer, Dura Mater, is a tough, leather-like tissue.
• Arachnoid Membrane looks like spider's web in cross-section
• The third layer, Pia Mater, is a transparent membrane sticking closely to the brain's outside.
• Infection in the meninges can lead to meningitis, causing headache, stiff neck, incoherence, drowsiness, coma, and death.
• Tumors in the meninx's tissues are referred to as meningiomas.

Cerebrospinal Fluid (CSF)

• CSF serves as a protective fluid around the brain and spinal cord, having a composition similar to blood plasma.

• CSF allows the floating of the brain within the skull and flows through the subarachnoid space (between arachnoid membrane and pia mater), central canal (small central channel running the length of the spinal cord), and cerebral ventricles (four large internal chambers).

• CSF produces networks of capillaries called the choroid plexus, that protrude into the ventricles from the pia mater.

• New CSF processes on average 3 times daily

• CSF's key purposes include cushioning the brain and preventing neurons from responding to pressure maladaptively.

• Hydrocephalus, or "water on the brain," results from CSF blockage by a tumor, causing fluid buildup in the ventricles, expanding them and potentially leading to mental retardation in children.

• Treatment of hydrocephalus includes draining excess fluid from the ventricles or removing the obstruction.

Blood Supply

• The brain receives nutrients through the blood supply via the carotid arteries (sides of neck) and vertebral arteries (back of skull).
• The brain cannot store energy and is dependent on an uninterrupted blood supply.
• Significant brain damage occurs in less than 3 minutes after the heart stops.
• Brain death is the definition of death, parts of the brain that don't have a Blood Brain Barrier include: Pituitary gland, Median eminence, Area postrema, Preoptic recess, Paraphysis and the Pineal gland
• Ischemia is a lack of oxygen while Hemorrhagic is bleeding.

Nervous System Divisions

• Central Nervous System (CNS):
• Includes the brain and spinal cord.
• Tissues are encased in bone and covered in 3 layers of membrane.
• Cells in the CNS do not regenerate.
• The CNS utilizes cerebrospinal fluid.
• Peripheral Nervous System (PNS):
• Consists of all nerves exiting the brain and spinal cord, carrying sensory and motor messages.
• Tissues not encased in bone and have 2 membrane layers.
• Cells in the PNS regenerate with recovery and do not use cerebrospinal fluid.
• Terms:
• A Nerve is described as a group of actions in the periphery, either from the CNS to a muscle or gland or from a sensory organ to the CNS.
• A Nucleus is a cluster of neuron cell bodies.
• A Ganglion is a cluster of neuron cell bodies.

Spinal Cord

• The spinal cord is CNS part within the vertebral column and extends from the medulla to the first lumbar vertebra.

• Spinal cords communicate with all the sense organs and muscles excluding those located in the head.

• The spinal cord is shorter than the overall vertebral column.

• It features a central canal running down the center.

• White matter consists of myelinated axons, Grey matter is H-shaped with densely packed with cell bodies and dendrites, including dorsal and ventral horns.

• Spinal nerves attach in pairs at 31 levels of the spine: one on the left and one on the right.

• Each spinal nerve breaks down near the cord, its axons join via the dorsal or ventral root.

• Axons from sensory neurons are in the dorsal roots, they carry information about touch, position, pain, and temperature.

• Cell bodies are grouped together outside the cord to form the dorsal root ganglia. Axons from motor neurons are in the ventral roots for movement and cell bodies inside ventral

• Has 8 cervical nerves serving the head, neck, and arms. Has 12 thoracic nerves, serving most of the torso, 5 lumbar nerves serving the lower back and legs and 5 sacral nerves that serve backs of legs and genitals; there's also a coccygeal nerve

• Quadriplegia, due to cervical damage will cause a loss of sensation and motor function in the arms, legs, and torso.

• Paraplegia is from lumbar-level damage causing a loss of sensation and motor function in the lower torso and legs; arms and upper torso are retained.

The Brain

• The brain divides into three sections: hindbrain, midbrain and forebrain.

Hindbrain

• The hindbrain is the posterior part of the brain containing the medulla, the pons, and the cerebellum.
• Medulla (or Medulla Oblongata) is the most posterior division of the brain. Important structures that are included are the Reticular formation, a complex of ~100 tiny nuclei that is associated with regulation of sleep and arousal. The Cranial nerves originating in the medulla control vital reflexes such as breathing, heart rate, vomiting, salivation, coughing, and sneezing.
• In the Pons are the Cochlear nucleus which receives information about sounds, while the Vestibular nucleus receives information about the rotation and position of head. Other regions involved are the Raphe nuclei which regulate sleep and arousal, and the Locus Coeruleus which only participates in arousal
• The Cerebellum assists in the coordination and control of movements and balance. Damage also affects skilled movements and speech control.

Midbrain

• It divides into the Tectum (or dorsal/top half) and tegmentum.
• Tectum is the Latin word for "roof.".
• The Tectum is composed of two pairs of bumps called colliculi/little hills. These include:
  • The inferior colliculi, associated with auditory reflex and localization of sounds.
  • Superior colliculi are for visual-motor function (to direct the body's orientation.)
• The Tegmentum is intermediate level/ventral as it is latin for "covering."
• Significant structures inside the tegmentum are Periaqueductal Gray, a gray matter involved in analgesia and specifically on perception of pain. Substantia Nigra contains "black stuff" composed of motor nuclei which are important component of a sensorimotor system. The degeneration of this area causes Parkinson disease Additionally, the Red Nuclei communicates motor information between spinal cord and cerebellum.

Forebrain

• The forebrain divides into thalamus, hypothalamus, cerebral cortex, limbic system, and basal ganglia.
• The Thalamus is has mostly sensory system structure that transmits signals to the cerebral cortex.
• Damage can cause comatose or seizures in the patient
• The Hypothalamus is located in the anterior of thalamus which regulates emotions and reactions regulation of motivated behavior - fleeing, feeding, fighting,Directs Autonomic Nervous System (ANS) and portion of PNS involved in regulation of glands/organs
• The Pituitary gland is located in hypothalamus, regulation the release of hormones; and optic chasm - point which optic nerves from each eye come together. Damage causes abnormalities on motivated behaviors and issues related to other bodily organs.

Limbic System

• The limbic System (Border) includes the hippocampus (seahorse) that deals with memory and learning but also long term declarative memory functions. If there is damage, anterograde amnesia occurs.
• Additionally has Amygdala for fear rage and aggression. if damaged inability to respond in appropriate situations. and is located on the margins of cerebral cortex Other regions that are linked are Cingulate cortex for emotions and feelings: Electrical Stimulation results in pleasure while Lesion results to uncontrollable rage and attack behavior, and also Olfactory bulbs that receive and process information. Finally the Mamillary bodies controls direction/memory and the Fornix that are pathways that connect these aforementioned regions for overall memory function.

Basal Ganglia

• Subcortical structures lateral to thalamus include motor function
• Caudate nucleus + Putamen + Globus pallidus + Nucleus accumbens (reward experience); damage leads to Parkinson's/huntington's/ADHD

Cerebral Cortex

• The cerebral cortex is composed of gray matter and white matter.

• Cerebral Cortex covers the cerebrum or "brain" in latin; while cortex is described as "bark" as its Outer portion

• Contains convoluted (furrowed) gyrus patterns on the Longitudinal Fissure; which when removed has been tested and has been shown to caused seizures

• Fissures- large furrows.

• Sulci- small furrows.

• Gyri- ridges or hills between the sulci or fissures.

• Divided Into Left and Right hemisphere - connected by cerebral commissures

Lobes

• The cerebral cortex has Lobes divided by Central and Lateral Fissures.
• They often do not have a Functional organization.
• Named after the skull bones
• Laminae that are cell bodies that runs parallel and are seperation
• Columns- are set of cell that have same properties
• The three Cortex functional areas: Sensory, Motor and Association

Occipital Lobe

• The location is Other wise of central sulcus. The primary visual cortex cortex provides the initial cortical data processing (visual). Damage in cortex is normal has normal eyes visual ability only pupillary reflexes- blindness: if hemisphere causes visual field is damaged as well.

Parietal

• Between Lobe Central sulcus also - Primary Somatosensory Cortex Analyses senses touch Pain, position temp & other parts Body Directing to attention" & Process touch ,monitor movements Eye & Position body

Temporal

• Lateral Side each hemisphere is
• Primary Hearing Cortex initial Sound provides Process Info , Cortex visual ident patterns and medial which holds memories for movement functions/spacial

Frontal

• extends Anterior limit brain
• Pre M cortex highest command for brain Motor also & Broca that speech
• Prefrontal the planning working memory or behavior when in this region is hurt it causes personality changes lack of emotion

###Somatic Nervous System (SNS)

• Interacts and moves motor function skeletal muscles from External environment + sensory

Autonomic Nervous System (ANS)

• Regulates body ,regulatory : circulation digestion
• Contains sympathetic- action energy or action ; parasympathetic conserves energy.
• Each has Automatic nerve that receives information and feedback through nerves ; or the lack thereof.

Cranial Nerves

• Oculomotor
• Olfactory
• Trochlear
• Optic
• Trigeminal
• Abducens
• Facial
• Auditory
• Glossopharyngeal
• Vagus
• Spinal Accessory
• Hypoglossal