Nervous Systems Overview of a Nervous System Overview

Nervous Systems

Overview of a Nervous System

Overview of a Nervous System • Sensory Input – conduction of signals from sensory receptors – PNS • Integration – environmental information is interpreted – CNS (brain and spinal cord) • Motor Output – conduction of signals to effector cells – PNS

Neurons

Neurons • Cell body – nucleus and organelles • Dendrites – short and branched – toward cell body • Axons – long and unbranched – away from cell body

Axons • Myelin Sheath - insulating layer • Node of Ranvier - gaps between Schwann Cells • Synaptic Terminals - neuron ending

Clusters of Neurons • Ganglion – Cluster of nerve cell bodies in the PNS • Nuclei – Cluster of cells in the brain

Supporting Cells • Glia (glue) – Oligodendrocytes • Form myelin sheath in brain – Schwann Cells • Form myelin sheath in the PNS

Reflex • Sensory neuron to a motor neuron

Neural Signals • Membrane Potential • Sodium-Potassium Pump

Threshold Potential

Resting State • Both sodium and potassium activation gates are closed • Interior of cell is negative

Depolarization State • Sodium activation gates are opened on some channels • Interior of cell becomes more positive

Rising Phase of Action Potential • Most sodium activation gates are opened • Potassium activation gates are still closed

Falling Phase of Action Potential • Inactivation gates on sodium channels are closing • Activation gates on potassium channels are opened • interior of cell becomes more negative

Undershoot • Both gates to sodium channels are closed • Potassium channels are closing • Membrane returns to its resting state

Propagation of the Action Potential • Localized event • First action potential’s depolarization sets off second action potential • Travels in one direction due to refractory period

Salatory Conduction • Action Potential jumps from node to node • Speeds up signal from 5 m/sec to 150 m/sec

Communication Between Synapses • Electrical Synapses – gap junctions allow for direct transfer of action potential (used during escape responses) • Chemical Synapses – uses neurotransmitters

Chemical Synapse

Chemical Synapses • Action potential triggers an influx of calcium • Synaptic vesicles fuse with presynaptic membrane • Neurotransmitter released into synaptic cleft • Neurotransmitters bind to receptors and open ion channels on postsynaptic membrane which sets off new action potential • Neurotransmitters are degraded by enzymes or removed by a synaptic terminal

Neurotransmitters

Vertebrate Nervous System

Central Nervous System • Ventricles (4) – Cerebrospinal fluid • White Matter – Made up of axons • Gray Matter – Made up of dendrites

Peripheral Nervous System

Peripheral Nervous System • Autonomic Nervous System regulates the internal environment (usually involuntary) • Somatic Nervous System regulates the external environment (usually voluntary)

Autonomic Nervous System

Autonomic Nervous System • Sympathetic Division – Flight or fight response • Parasympathetic Division – Rest or digest response

Brain

The Brainstem • The Medulla Oblongata and the Pons controls breathing, heart rate, digestion • The Cerebellum controls coordination of movement and balance

The Midbrain • The Midbrain receives, integrates, and projects sensory information to the forebrain

The Diencepholon • Forebrain – Epithalamus • Includes the pineal gland the choroid plexus – Thalamus • conducts information to specific areas of cerebrum – Hypothalamus • produces hormones and regulates body temperature, hunger, thirst, sexual response, circadian rhythms

The Telencepholon • Cerebrum – with cortex and corpus callosum • higher thinking

Cerebrum

Cerebrum

Cerebrum

Limbic System • Regulates emotions – Association with different situations is done mostly in the prefrontal lobe

Memory • Short Term – Done in the frontal lobe • Long Term – Frontal lobes interact with the hippocampus and the amygdala to consolidate

Sensory Receptors • • • Mechanoreceptors Pain Receptors Thermoreceptors Chemoreceptors Electromagnetic Receptors

Sensory Receptors • Mechanoreceptors • Pain Receptors • Thermoreceptors

Sensory Receptors • Chemoreceptors

Sensory Receptors • Electromagnetic receptors

Evolution of the Eye • Complex eyes have developed many times

Evolution of the Eye • All light-sensitive organs rely on photoreceptor systems employing a family of proteins called opsins. Further, the genetic toolkit for positioning eyes is common to all animals: the PAX 6 gene controls where the eye develops in organisms ranging from mice to humans to fruit flies

Photoreceptors • Eye cups (ocelli) - light detection • Genetic basis that started as a light detector 600 mya • During the Cambrian explosion around 540 mya two types of eyes arose

Photoreceptors • Compound Eyes made up of ommatidia that helps detect movement

Photoreceptors • Camera Type Eyes – Evolved several times – Hagfish eye – Lamprey eye – Jawed vertebrate eyes

Single Lens Eye • • Sclera (white) Cornea (clear) Choroid (pigmented) Iris (color of eye) Retina (rods and cones) Pupil Fovea (focal point) Blind spot

Photoreceptors Scars of Evolution 1. inside out retina that forces light to pass through the cell bodies and nerves before hitting the retina 2. blood vessels across the retina that cause shadows 3. nerve fibers that exit causing a blind spot

Focusing • Near vision – ciliary muscle contracted – lens becomes more spherical • Distance vision – ciliary muscle relaxed – lens becomes flatter

Visual Problems • Near-sightedness (myopia) – eyeball too long / focal point in front of fovea • Far-sightedness (hyperopia) – eyeball too short / focal point behind fovea • Astigmatism (blurred vision) – misshapen lens or cornea

Hearing and Equilibrium

Hearing Organ • Outer Ear – pinna and the auditory canal – tympanic membrane • Middle Ear – malleus, incus and stapes – oval window • Inner Ear – cochlea with the Organ of Corti • with a basilar membrane and hair cells • Eustachian Tube

Sound • Volume – amplitude of sound wave – vibrates fluid in ear and bend hair cells which generates more action potentials • Pitch – frequency of sound wave

Equilibrium • Utricle and Saccule • Semicircular Canals – used to detect body position and movement

Chemoreception • Taste Buds – sweet (tip), salty (behind), sour (sides), bitter (back of tongue)

Chemoreception • Olfactory receptors cells – upper portion of nasal cavity

The Cost of Locomotion

The Cost of Locomotion • Locomotion must overcome two forces: – gravity – friction • Swimming is more efficient than running – runner must overcome gravity • Larger animals travel more efficiently than smaller animals • Flight is the most costly (per minute)

Cooperation of Muscles and Skeletons • Muscles always contract • Muscles attached in antagonistic pairs

Skeletal Muscles • Muscles are made up of muscle fibers • Fibers are made up of myofibrils • Myofibrils are made up of myofilaments – thin filaments (actin) – thick filaments (myosin)

Sliding Filament Model • Sacromeres (basic functioning unit) – Z lines (border of sacromeres) – H zone (center of sacromere) – I band (only thin filaments) – A band (length of thick filaments)

Sliding Filament Model • During contraction, thin and thick filaments slide past each other – I band H zone decreases in size • Caused by myosin head creating cross bridge with actin fiber and then moves by using ATP