Nervous System: Structure and Function

Functions Localized in the Nervous System Concepts

• Nervous systems are made of neurons and glia
• Neurons create and perform electrical impulses
• Glia in the form of macroglia control neuron activity, and provide support
• Microglia, phagocytic cells, are the major immune responses of the nervous system
• Neurons are excitable cells, communicating along actions
• Nerves are bundles of axons, which provides information
• Neurons provide information to the central nervous system, and from it to other organs
• Central nervous systems consist of the brain and the spinal chord
• Peripheral nervous systems are nerves that reach all tissues
• The enteric nervous system can be found in the gut

Peripheral nervous system divisions

• The afferent portion brings information from sensory receptor cells to the CNS
• The efferent portion carries information from the CNS to muscles and glands
• Both have conscious and unconscious divisions

Vertebrates and Brain Size

• Body and brain size in vertebrates are typically correlated
• Higher primates are above regression line for this
• The cerebral cortex in humans is the largest area of the brain and made even larger with convolutions
• The cortex is devoted to information integration

Brain Development

• The CNS develops from the neural tube of an embryo
• The anterior part develops into 3 sections, the hindbrain, the midbrain, and the forebrain
• Finally, the spinal chord is formed
• Information in the adult nervous system follows paths that emerge from the neural tube
• The midbrain develops functions that integrate sensory information, and coordinates motor responses
• The Hindbrain contains the medulla, pons and cerebellum
• Medulla and pons control physiological functions, like breathing
• The midbrain, medulla, and pons are the brainstem
• All information travelling between the spinal chord, and higher brain areas needs to pass through the brainstem
• Cerebellum takes care of muscle activity and balance

Cranial Nerves

• The brainstem regulates autonomic functions with 12 pairs of cranial nerves
• Cranial nerves include the olfactory, optic, and auditory nerves
• Cranial nerve X, the vagus nerve, goes to the body cavity, connecting to multiple organs, like the heart and gut.
• Nucleus refers to distinct group of CNS neurons
• The brainstem nuclei keep higher brain areas awake or allowing them to sleep
• Central part the brainstem is called the reticular activating system
• Paralysis may results from Damage to the brain or spinal cord below the reticular activating system
• Damage above the level of the reticular activating system may cause coma

Spinal Cord

• Spinal cords provide information from the brain and preform integrative functions
• Peripheral Nervous system provides information, and the cord sends out commands like the knee jerk reflex
• Spinal cords coordinate complex behavior like withdrawal reflexes
• Anatomy of spinal chord consists of grey matter to the core, containing cell bodies of spinal neurons
• White matter surrounds grey area, containing axons conducting information
• The spinal chord contains information between organs and brain
• The spinal chord responds by signalling motor commands
• The spinal chord has reflux, and autonomic functions (sympathetic, parasympathetic)

The Forebrain

• It is formed into two region, the diencephalon, and the telencephalon
• Diencephalon contains the thalamus and hypothalamus
• Telencephalon contains the cerebral hemisphere
• The outer layer is cerebral cortex contains a thin layer of cell bodies
• Vertebrate evolution is telencephalization, when telencephalons increase in size/complexity
• The chord forebrain consists of the thalamus, communicating sensory information to the cortex
• The hypothalamus takes care of many homeostatic functions
• The diencephalon is surrounded by older phylongentic structures of the telencephalon, the limbic system.
• Hypothalamus is in direct contact with the pituitary gland, regulating hormone release
• Active hormones are released in the posterior lobe

Limbic system

• Limbic systems are responsible for instincts, memories formation, thirst and hunger and sexual behavior
• The Amygdala is included in fear and fear memory
• The Hippocampus, moves short to long term memory

The Cerebral Cortex

• The cerebral cortex possesses large surface area
• The cerebral cortex can be described by ridges (gyri) and valleys (sulci).
• The convolutions fit the skull with the cortical surface
• The central sulcus separates the frontal and parietal lobes
• One hemisphere controls the opposite side except for the head

Lobes of the Brain

• The lobes of the brain, separated as follows:
  • The Frontal Lobe
    • Central sulcus divides frontal and parietal lobes
    • The primary motor cortex controls muscles in body areas in front of central sulcus
    • Body parts with motor control like face and hands have representations
    • Frontal lobe controls feelings and planning
    • The lobe carries out executive functions like planning, decision making, personality expression, controlling social behavior, determining different thoughts, determining consequences of actions
  • The Temporal Lobe
    • It gains and processes auditory information
    • The lobe is connected to association areas
    • higher processing of visual information is made, such as identifying objects.
    • Agnosias: inability to ID objects.
    • The lobe may cause inability to recognize faces or speech
  • The Parietal Lobe
    • It is formed to the Primary somatosensory motor cortex right behind the central succus
    • The parietal lobe is meant to receive pressure and touch from the thalamus
    • All body surfaces that have densities of mechanoreceptors possess representation
  • The Occipital Lobe
    • Processes visual information
    • It is connected to other association areas
    • It help understanding the realm of visuals
    • It translates visuals into language.
  • Insular Cortex
    • It gain wide range of afferent information
    • Integration occurs through physiological information across the human body to make impression of “feeling"
    • Damage to parietal lobe can result in neglect syndrome, where the affected is unable to ID with side of body.

Language

• Broca’s area in the frontal lobe is damaged, resulting in slow or lost speak, and retains understanding language
• Wernicke’s area, in the temporal lobe, which results speaking senselessly
• a person may still be able to produce speech
• Angular gyrus is nearby, which provides integrating spoken and written communication
• Language shows an 97% result in the left brain hemisphere.
• An aphasia in ability to use or understand language.

Autonomic Nervous System (ANS)

• Contains PNS components and the CNS
• Controls involuntary functions
• Two divisions work such as sympathetic (fight or flight) and parasympathetic (rest & digest)
• EFFERENT pass begin with preganglionic cholinergic neurons. cells bodies. axons connect to ganglion near the CNS
• POSTganglionic neurons synapse with cells to organs
• Sympathetic Postganglionic neurons include Norepinephrine (as a neurotransmitter)
• Parasympathetic Postganglionic : Acetylcholine (as a neurotransmitter)
• Sympathetic preganglionic nerves near the thoracic & lumbar spinal chord and chains
• All parasympathetic preganglionic neurons near brain and sacral near ganglia

Sleep patterns

• EEG (electroencephalogram, EMG (Electromyograms), and EOG (electrooculogram) are connected to sleep
• Mammals other than humans bear two cycles with low wave sleep and jerking movement of REM as states Humans bear the NREM (3 stages) deep state rest and recovery
• REM stage contain Dreams and activity
• Non–rapid eye movement contains slow rolling eyes. decline and metabolism.
• Rapid eye movement contains rapid twitching muscles, erection, blood, and paralysis

Memory

• Learning: a process by which new information is acquired
• Memory: refers to the encoding, storage, and retrieval
• High frequency electrical stimulation (LTP): make other circuits more responsive
• Low Frequency electrical stimulation (LTP) - Reduce circuits and more fundamental memory
• Memories need other regions
• Memories need synapses to adapt.
• Mechanism of loss may occur if memories are lost in an injured brain.
• Hippocampus have important with memories
• Declarative memories involves events and things
• Spatial information can change the network and rate that occurs