Chapter 2 Exploring the Nervous System

Anatomical Views Horizontal section - Shows structures viewed from above Sagittal section - Divides structures into right and left parts Coronal section - Shows views from the front

Anatomical Directions Anatomical directions are used for locating structures with the body: Anterior - toward the front Posterior - toward the rear Ventral - toward the belly Dorsal - toward the back Rostral - toward the head Caudal - toward the tail Medial - toward the midline Lateral - away from the midline Superior - above a structure Inferior - below a structure

The Importance of the Nervous System 1)Detect stimuli in the environment 2)Determine the significance of the environmental stimuli 3)Make a decision based on the stimuli 4)Execute a response

Organization of the Nervous System: Two Major Divisions Peripheral Nervous System (PNS)  Detects environmental information inside and outside the body, which is transmitted to the CNS  Executes responses to stimuli Central Nervous System (CNS)  Recognizes and analyzes information from the PNS  Makes and transmits decisions to glands, organs, and muscles for execution

Cells of the Nervous System: Nerve cells – neurons perform the information processing and communication functions of the nervous system Glial cells - supportive cells in the nervous system. The glial cells surround neurons and provide support for and insulation between them.

Cells of the Nervous System: Neurons Perform information processing and communications functions of the nervous system  Consist of three major parts: 1. Soma - contains nucleus, mitochondria, and ribosomes 2. Dendrites - portions of the neuron that transmit information toward the cell body 3. Axon - a structure on the neuron which transmits information away from the cell body

Cells of the Nervous System: Terminology Groups of neurons form four functional groups: A collection of axons  Nerve – in the Peripheral Nervous System (PNS)  Tract – in the Central Nervous System (CNS) A collection of cell bodies  Ganglion – within the PNS  Nucleus - within the CNS

Cells of the Nervous System: Functional Types of Neurons Sensory neurons - carry information to the CNS Interneurons - connect sensory and motor neurons or communicate with other interneurons Motor neurons - carry information from the CNS to muscles, organs, and glands to control their functioning.

Physical Types of Neurons

Cells of the Nervous System: Types of Synapses Axodendritic - the axon synapses with dendrites of another neuron Axosomatic - the axon synapses with the cell body of another neuron Dendrodendritic synapse - occurs when the dendrites of one neuron synapses with the dendrites of another neuron Axoaxonic synapse - the axon of one neuron synapses with the axon of another neuron Neuromuscular junction - the axon synapses with a muscle

Cells of the Nervous System: Glial Cells Glial cells One-tenth the size of neurons Ten times as numerous as neurons Types of Glial cells Astrocytes - provide physical support to neurons, nourishment and other functions. Microglial cells - remove debris Oligodendrocytes - produce myelin which covers the axons of neurons in CNS Schwann cells - produce myelin which covers the axons of neurons in PNS

Myelination

Organization of the Nervous System: The Peripheral Nervous System Detects internal and external environmental information; relays information to CNS Executes CNS’ decisions in muscles, glands and organs Spinal nerves and Cranial nerves Peripheral Nervous System includes:  Somatic Nervous System - Includes both sensory and motor systems  Autonomic Nervous System - Regulates the internal environment

The Peripheral Nervous System: Somatic Nervous System Enables us to interact with the physical environment Afferent neurons – transmit messages from sensory receptors to the CNS Efferent neurons – transmit messages from the CNS to skeletal muscle Spinal nerves – 31 pairs of nerves that send messages to/from the brain thru the spinal cord Cranial nerves – 12 pairs of nerves that link sensory receptors in the head directly to the brain and the brain to certain muscles

Cranial Nerves

The Peripheral Nervous System: Autonomic Nervous System Primarily efferent neurons Controls internal environment - glands and internal organs Consist of two parts that are typically antagonistic: Sympathetic Parasympathetic

The Autonomic Nervous System

Organization of the Nervous System: The Central Nervous System  Recognizes and analyzes information received from the PNS  Makes and transmits decisions to glands, organs, and muscles for execution Central Nervous System includes:  Spinal cord - responsible for limited analysis and decision making, transmits information to and from the brain.  Brain - responsible for analyzing sensory information and making appropriate responses to it.

The Protective Features of the Central Nervous System Protecting the spinal cord Vertebral Column - outer bony covering that encases the spinal cord Protecting the brain Skull - outer bony covering that encases the brain Ventricular system Meninges protects both Dura matter Arachnoid matter Pia mater

The Central Nervous System: Spinal Cord Serves as a conduit to and from the brain Controls spinal reflexes

The Central Nervous System: The Brain Three main functions: Recognizing stimuli detected by the PNS Analyzing the information Initiating the appropriate response Three main areas: Hindbrain Midbrain Forebrain

The Brain: The Hindbrain Myelencephalon Medulla oblongata, which controls basic life functions Metencephalon  Pons - a “bridge” for fibers passing from one side of the brain to the other. Sensory fibers, fibers from the cortex to cerebellum, and fibers that relay information on sleep, arousal and dreaming pass through it.  Cerebellum - involved in the development and coordination of movement Reticular formation  Involved in arousal, begins in the medulla and extends to other areas of the brain

The Hindbrain

The Brain: The Midbrain Mesencephalon Tectum - relays visual and auditory information and controls simple reflexes, eye and ear orientation movements Tegmentum - substantia nigra - integration of voluntary movements red nucleus - controls basic body movements reticular formation - controls arousal and consciousness Brain stem = midbrain + hindbrain not including the cerebellum

Diencephalon Epithalamus - contains habenula (olfactory functions) and pineal gland Thalamus - major relay station for sensory information Hypothalamus - detects need states, controls the autonomic nervous system, and controls pituitary hormone production and release Pituitary - regulates other glandular activity of the body; often called the “master gland” The Brain: Forebrain

The Diencephalon

Telencephalon Limbic System  The limbic system is a group of structures surrounding the brain stem.  The limbic system structures include the amygdala, cingulate gyrus, and hippocampus.  Governs emotions such as anger, fear, and happiness, and is involved in the storage and retrieval of memories. The Brain: Forebrain

The Limbic System

The Brain: Forebrain Telencephalon Basal Ganglia - have widespread connections to the cortex and forebrain and are involved in the initiation of voluntary movements, maintaining muscle tone and posture

The Brain: Forebrain Telencephalon Cerebral Cortex - the convoluted outer layer of the forebrain that processes sensory information, controls thinking, decision making, stores and retrieves memory, and initiates motor responses The cortex is divided into two hemispheres connected by the corpus callosum and each hemisphere has four lobescorpus callosum

The Cerebral Cortex

The Brain: Lobes of the Cerebral Cortex Occipital lobe - primary function is the analysis of visual information Parietal lobe - The anterior portion analyses sensory information such as pain, pressure and body position. The posterior portion is involved in spatial perception. Temporal lobe - includes the primary auditory cortex, a visual area and language centers

The Brain: Lobes of the Cerebral Cortex Frontal lobe -  Broca’s area - area for programming and sequencing of motor movements for speech production Broca’s area  Prefrontal cortex - controls complex intellectual functioning such as planning and sequencing of behavior.  Motor cortex - area of the frontal lobe anterior to the central sulcus.

Representation of body parts in the somatosensory cortex and motor cortex